Her lawyers are from the New Civil Liberties Alliance, a libertarian-leaning nonprofit that counts among its financial backers Donors Trust, a group with ties to the billionaire Leonard A. Leo, who is a co-chairman of the Federalist Society.

The Federalist Society is an influential legal group that advised Mr. Trump through the confirmation of justices he appointed to form the current conservative supermajority on the Supreme Court, though some in Mr. Trump’s circle came to believe that its leaders were out of step with the president’s political movement.

Another donor to New Civil Liberties Alliance is Charles Koch, the billionaire industrialist and Republican megadonor.

In what appeared to be the first tariff-related lawsuit against the Trump administration, the founder of Simplified, Emily Ley, argued that President Trump overstepped his authority in February when he first imposed new import taxes on Chinese goods. Since then, China has retaliated with its own tariffs, and Mr. Trump has escalated the fight with more levies. All Chinese imports face a minimum tariff rate of 145 percent as of Thursday, a dramatic increase.

Tax filings since 2017, when the New Civil Liberties Alliance was founded, show that it has received millions in financial support from a network of powerful conservative groups including both the Charles Koch Foundation and Donors Trust, which has financial ties to Mr. Leo.

On Wednesday, after days of turmoil on the stock and markets, Mr. Trump announced a three-month reprieve on the punishing tariffs he had imposed on most of America’s major trading partners in an effort to redress trade deficits, leaving in place only a base line 10 percent tariff for all imports.

Still, the president has remained committed to ratcheting up the pressure on China, whose leaders have vowed to fight back.

While a number of top Republicans in Congress have expressed chagrin at the tariffs, only a few have second-guessed the president publicly.

But the lawsuit illustrates the growing divisions within the party’s elite between traditional conservatives who worry about the long-term effect of tariffs on the economy and Mr. Trump’s ideological allies, who have applauded his “by any means necessary” approach to reversing years of trade deficits.

Mr. Koch is no stranger to opposing Mr. Trump. The donor network he established with his brother David Koch attempted to finance challenges to Mr. Trump during the 2024 election cycle, steering around $70 million to Republican campaigns that were focused on moving away from the president’s priorities.

Both Mr. Koch and Mr. Leo have enjoyed considerable success in advancing conservative ideas and policy by paying for strategic lawsuits and doling out financial support through a network of right-leaning legal groups.

For its part, the New Civil Liberties Alliance has recently established its bona fides through a number of high-profile victories, often focusing on cases aimed at beating back regulations and advancing libertarian causes.

Just last year, the organization notched two prominent wins.

It represented the plaintiffs in a case that ultimately resulted in the Supreme Court dramatically curtailing the regulatory power of federal agencies. The 6 to 3 decision swept aside decades of precedent and handed the conservative legal movement a long-desired win in its efforts to pare back government regulation.

That lopsided split along ideological lines was made possible by the justices Mr. Trump appointed on advice from Mr. Leo’s Federalist Society.

Notably, the New Civil Liberties Alliance also helped reverse one of Mr. Trump’s policies from his first term — a ban on bump stocks that his administration imposed after a gunman using the device massacred 60 people in Las Vegas in the deadliest mass shooting in modern American history. The group represented a man challenging Mr. Trump’s ban and succeeded in convincing the Supreme Court to strike it down last year in another 6 to 3 decision.

The complaint filed on behalf of Ms. Ley, in Federal District Court for the Northern District of Florida, asked a judge to declare Mr. Trump’s China-related executive orders unconstitutional and to bar Customs and Border Protection from enforcing the tariffs.

It argued that Mr. Trump was circumventing Congress by unlawfully using the International Emergency Economic Powers Act of 1977 to impose the tariffs. The law gives the president the broad authority to regulate a variety of economic transactions following a declaration of national emergency.

In its complaint, the organization argued the law does not give Mr. Trump the power to impose tariffs by simply declaring that trade deficits constitute a national emergency, and if he is allowed to do so, he “will have nearly unlimited authority to commandeer Congress’s power over tariffs.”

“He would be empowered to declare a national emergency based on some long-running national problem, then impose tariffs purportedly in the name of that emergency — thus sidestepping the detailed constraints Congress has placed on the tariff authority it has granted,” the complaint said.

“Everybody wants to come and make a deal, and we’re working with a lot of different countries, and it’s all going to work out very well,” Mr. Trump said during a cabinet meeting. “I think it’s going to work out really, very well, but we’re in good shape.”

Mr. Lutnick chimed in: “We have so many countries to talk to. They have come with offers that they never, ever, ever would have come with but for the moves that the president has made demanding that people treat the United States with respect.”

But exactly which countries might strike a deal, and over what, remains unclear. For the most part, the deals that the Trump administration negotiates are unlikely to be comprehensive trade agreements, which can take years to broker and require congressional approval.

More limited deals may benefit some exporters, but not ultimately do much to help the U.S. economy or diminish the U.S. trade deficit, which Mr. Trump has targeted. Manufacturing, tech and retail business groups in Washington said Wednesday that they had heard no indications of deals coming together yet.

Meanwhile, the S&P 500 tumbled 3.5 percent on Thursday, with investors still feeling concerned about the volatility in Mr. Trump’s approach. Even with the 90-day pause that the president announced on Wednesday, the tariffs he has imposed on the world remain extremely high. Goods from China now face a minimum tariff rate of 145 percent, a drastic increase on a country that supplies much of what Americans buy.

After Mr. Trump’s tariffs announcement last week, foreign officials raced to Washington to try to forestall the levies. Administration officials said that more than 75 countries had reached out to them, and the U.S. trade representative, Jamieson Greer, met with officials from Europe, South Korea, Ecuador and Mexico on Tuesday.

Vietnamese officials had offered to preemptively cut their tariffs on American apples, cherries and ethanol, and brought along a term sheet to the meeting that detailed changes they were willing to make, Mr. Greer said.

Treasury Secretary Scott Bessent’s office on Thursday released a readout of the administration’s discussions with Deputy Prime Minister Ho Duc Phoc of Vietnam. Mr. Trump said last week that the United States had begun discussing tariff rates with Vietnam.

“During their talks, Secretary Bessent emphasized the importance of continued engagement with trade partners, and the need for quick, demonstrable progress to resolve outstanding issues,” the readout said.

That was about as specific as it got.

Mr. Trump tends to prefer speaking in vague terms, in part because it allows him flexibility to avoid being pinned down. But that lack of specificity, and lack of clarity about what the end game was, were part of why the tariffs announcements sent markets spiraling.

Kevin Hassett, the director of the National Economic Council, said he had spoken with the president of Switzerland on Thursday morning about a deal. He said that the Office of the U.S. Trade Representative “already had offers on the table for more than 15 countries.”

Mr. Bessent said he had spoken with representatives from Vietnam on Wednesday, and had a “good chat” with the Japanese ambassador at his house the previous night during a cherry blossom party.

Japan was at the front of the queue for a trade deal, followed by South Korea and India, Mr. Bessent said on Wednesday. He added that any trade agreements would be “bespoke” and “take some time,” because Mr. Trump wanted to be involved personally.

One person familiar with the discussions said that Japanese officials were angling for their country to have one of the first trade deals, but that talks could be more difficult because of longer-run disagreements in sectors like autos and steel.

Japan and the United States have long-running trade disputes going back to the 1980s — the era that Mr. Trump would like manufacturing in the United States to return to.

In Mr. Trump’s first term, he signed a “mini-deal” with Japan that addressed just a few sectors, and pursued the same type of limited agreement with India and other countries.

There are few signs that the United States will begin actively negotiating with China anytime soon, though Mr. Trump said on Thursday that China’s leader, Xi Jinping, “has been a friend of mine for a long period of time.”

“We’ll see what happens with China,” Mr. Trump said. “We would love to be able to work a deal.”

Tony Romm contributed reporting.

But the announcement on Thursday barely caused a ripple among Hollywood studios. Because of China’s increased censorship and control over the timing and size of the distribution of U.S. releases, the country is no longer as lucrative a market as it used to be.

China prefers to release its own local-language films, like “Ne Zha 2,” an animated film that debuted in January and became the world’s highest-grossing film released in China, with $1.2 billion in box office revenue.

The downward trajectory of American film franchises in China has been significant. Last year, “Godzilla x Kong: The New Empire” was the only U.S. movie in the Top 10 of China’s box office. In 2023, no American film entered the Top 10.

Take the “Mission Impossible” franchise, as an example. In 2018, “Mission Impossible: Fallout” generated $181 million in China, the second-largest market after the United States. The 2023 film in the series, “Mission Impossible: Dead Reckoning Part One,” earned only $48 million.

It’s unclear whether the newest “Mission Impossible” film, starring Tom Cruise and set to debut in the United States on May 23, will even be released in China. Paramount Pictures, the studio behind the film, declined to comment.

Thursday’s drop brought a continuation of the chaotic trading conditions and sharp losses that have characterized the stock market since President Trump’s announcement last week of steep tariffs across the nation’s trading partners. As stocks slid again, the wild swings in government bonds caught the attention of policymakers who are watching to ensure that one of the most crucial financial markets in the world continues to function smoothly.

Investors had welcomed Mr. Trump’s 90-day reprieve on higher tariffs, and the market soared within minutes of the announcement on Wednesday. The pause applied to all countries except China, which investors had thought would face an import tax of 125 percent.

But stocks began to drop on Thursday morning as analysts noted that even with the tariff pause, countries still faced a new blanket 10 percent tariff — already much higher than before. Tariffs recently imposed on cars and auto parts, and steel and aluminum, would also remain in place. Then the White House clarified that the new 125 percent tariff on Chinese imports was on top of earlier 20 percent tariffs, taking the number to 145 percent.

“Despite the good news, policy uncertainty remains elevated and will act as a drag on the U.S. economy,” James Rossiter, the head of global macro strategy at TD Securities, wrote in a note. “Firms will struggle to plan.”

President Trump signaled an openness to negotiating with countries over the nearly across-the-board 10 percent tariff he had imposed. While describing it as a “base line” at a cabinet meeting on Thursday, he also seemed to say it could be subject to change. “It depends on what they’re adding,” he said.

Chief executives have begun to warn that uncertainty is challenging enough.

On Wednesday, Delta Air Lines said a lack of clarity about the economy prevented it from telling investors how much money it expected to make this year. Delta’s stock price tumbled more than 11 percent on Wednesday.

Economists also warned that the remaining tariffs on China would still have enormous repercussions for the American economy. Many public companies whose stocks and shares trade on the open market rely on imports from China. The clothing retailer Nike fell over 8 percent Thursday.

Wendong Zhang, an assistant professor of applied economics and policy at Cornell, pointed out that “many products that the U.S. imports are predominantly from China,” including 73 percent of smartphones, 78 percent of laptops, 87 percent of video game consoles and 77 percent of toys. “Resourcing from other countries will take time and result in much higher costs,” Mr. Zhang said in an interview on Wednesday.

Few corners of the stock market were spared. More than 80 percent of the stocks in the S&P 500 ended the day lower. The energy sector led declines as oil prices tumbled, another harbinger of slowing global growth. The U.S. dollar weakened 1.7 percent against a basket of currencies of its major trading partners, its worst day of the year so far.

CarMax tumbled 17 percent, among the worst performing stocks in the index, after the company said it had become a lot more challenging to forecast what was ahead.

“We are focused on growing the business, and we continue to make progress toward our long-term goals. However, we are removing the time frames associated with them given the potential impact of broader macro factors,” CarMax said in a statement as it reported quarterly results. Analysts expect that the 25 percent tariffs on imported cars that went into effect last week is likely to raise car prices, lower sales and cause other disruptions to the auto industry.

Rating agencies that score corporate debt based on how risky it is have begun to warn of rising defaults amid the economic fallout from tariffs. Measures of corporate borrowing costs have risen in recent days, a sign that lenders see more risk emerging for businesses.

The S&P 500 is again approaching a bear market, defined as a drop of more than 20 percent from its recent peak and a line in the sand for investors that marks a period of extreme pessimism.

The index has fallen 14.3 percent since its mid-February high. The tech-heavy Nasdaq Composite index and the Russell 2000 index of smaller companies have already dropped into a bear market.

Officials at the Federal Reserve are keeping close tabs on recent gyrations in financial markets, especially after a sell-off across U.S. government bonds earlier this week, which undermined their status as a place for investors to shield themselves during market storms.

Government bonds held steady on Thursday. The benchmark 10-year Treasury yield, which underpins borrowing across the economy, has risen from less than 4 percent on Friday to roughly 4.4 percent on Thursday.

Jeff Schmid, president of the Kansas City Fed, said the Fed was watching markets “by the minute” to “make sure that the transactions and liquidity keep flowing.” He added that the disruptions in Treasury markets this week had been “really instructive.”

Concerns have mounted that highly leveraged bets that seek to profit from the small difference in price between cash bonds and derivatives are exacerbating volatile markets. Such trades, popular among some hedge funds, have attracted the attention of regulators in the past for contributing to bouts of volatility.

Beth Hammack, who is now president of the Cleveland Fed after working at Goldman Sachs for decades, described U.S. markets as “strained but functioning” on Wednesday.

Wall Street’s slumped after major benchmarks in Asia and Europe ended Thursday sharply higher. In Asia, benchmark indexes rose more than 9 percent in Taiwan and Japan and 6 percent in South Korea. In Europe, the Stoxx Europe 600 index jumped more than 5 percent. The markets in Germany and France gained more than 5 percent.

The Chinese government has taken steps to stabilize its markets. State-owned companies announced on Tuesday that they were buying back some shares, a move that typically helps push stock prices higher. On Thursday, an influential state media outlet published a commentary saying it was a good time for the central bank to lower interest rates and take other steps that would support the economy.

Talmon Joseph Smith and Colby Smith contributed reporting.

Chefs who had been furiously calling their suppliers, stockpiling imported ingredients ahead of what seemed certain to be drastic price jumps, got a temporary reprieve on Wednesday. Hours after they’d gone into effect, Mr. Trump put on hold a patchwork of tariffs that targeted 57 countries with rates ranging from 11 to 51 percent. For three months, he declared, all imports would be hit with a flat 10 percent tariff except products from China, which face tariffs that have vaulted to 145 percent. Nobody knows what will happen after the three months are up.

If you are a restaurateur, none of this makes it easier to sleep at night, or to decide how much to charge for dan-dan noodles.

The National Restaurant Association has brought in supply-chain experts to advise restaurateurs on handling disruptions in the flow of imported seafood and vegetables. Owners who drew up their business plans in the era of free trade are asking whether they still make sense when governments around the world are using shrimp and wine as chips in a high-stakes poker game.

“Restaurants are the least profitable businesses on any Main Street in America,” said Sean Kennedy, the group’s executive vice president for public affairs. “With razor-thin profit margins, we are not equipped to deal with dramatic changes in food prices. Long-term tariffs leave us with no margin for error in holding menu prices as low as possible.”

On Tuesday, Jarrett Wrisley, a chef who serves dishes from southwestern China and northern Thailand at his restaurant Shan in Bozeman, Mont., ordered two pallets of dark soy sauce, Zhenjiang vinegar, Sichuan peppercorns, roasted sesame paste and other ingredients from China. At the time, he thought those products were facing a mere 104 percent tariff. Now, his suppliers say they aren’t sure they will be available in a month or two.

The bison, pork and other meats on Shan’s menu are raised in Montana. But nearly all the seasonings in Mr. Wrisley’s pantry are imported from China and Thailand, which until Wednesday had been threatened with a 34 percent tariff. After his suppliers raise their prices, he expects he will have to change some recipes. He said he can adjust to using Kikkoman soy sauce from factories in Wisconsin and California. There is no American-made substitute for many other ingredients, like fermented fava-and-chile paste from Sichuan.

“It’s aged in amphorae, it undergoes a long fermentation, the chiles are from Sichuan,” he said. “It can’t be reproduced in the United States. And I don’t think the point of this trade war is to onshore the production of niche Asian food products.”

One of his purveyors, Susie Kasem of ARJ Oregon, an importer in Portland, has heard from almost every restaurant she supplies with sticky rice, fish sauce and other Thai staples. She had to put limits on their orders because so many chefs were trying to load up their shelves before the tariffs went into effect.

“I’m so busy because everyone’s calling me today, yesterday, the day before,” Ms. Kasem said. “I don’t have any idea how to answer them.”

For restaurants that buy tequila or anything else from Mexico, Wednesday’s abrupt turnaround — the White House said that the 10 percent flat rate did not apply to Mexico and Canada a short time after Treasury Secretary Scott Bessent told reporters that it did — was all too familiar. Mr. Trump imposed a 25 percent tariff on Mexican goods in February, then removed it two days later. He did the same thing again in March.

Trucks carrying avocado, huitlacoche and other key ingredients that the Colorado chef Johnny Curiel uses in his four Mexican restaurants parked on the far side of border for several days in March as the dispute played out. Worried about future shortages, Mr. Curiel recently bought five tons of the imported corn that goes into his tortillas. He is negotiating directly with farmers who grow chiles and herbs in Mexico, a move that would hurt his longtime distributors.

“It’s not helping them, it’s helping me,” he said. “And that weighs heavy on me.”

Next month, a farmer north of Boulder will plant 10 acres of heirloom Cónico corn for him and another Colorado chef. They had been discussing the idea for some time, but finally decided to do it after Mr. Trump threatened Mexico with new tariffs early this year. Although those are now delayed, Mr. Curiel said that changing his supply chain will help him make plans.

“It’s great that it’s not going into effect,” he said. “But at the same time, there’s the uncertainty of not knowing what’s going to happen.”

That uncertainty was a sore topic for those who attended an annual chefs’ conference in Philadelphia earlier this week. After listening to peers who were worried that their costs would spike on Wednesday, the Chicago chef Erick Williams tried to bring some perspective to the coming crisis.

“When people say, “We’re screwed,’ I have a hard time believing it,” Mr. Williams said in an interview later. “If we managed to survive and adapt during the pandemic, then surely we have the capacity to navigate this moment, too.”

As he pointed out, restaurants sell more than food and drinks. They specialize in creating environments where people want to spend time together, swapping ideas and sharing cultures.

In many restaurants, though, the culture people come to immerse themselves in is one from another country. Imported ingredients aren’t the only thing on offer, but they help get customers through the door. Any policy that makes those items less profitable threatens to undermine the whole enterprise.

At Orion Bar in Brooklyn, N.Y., soju and instant ramen from South Korean serve as gateway drugs for other national exports like K-pop, K-movies and televised K-dramas.

“As someone who works a lot in sharing and spreading Korean culture, interest in it has been increasing and the tariffs are concerning because it potentially could affect that growth,” said Irene Yoo, the chef and an owner, the day before a 25 percent levy was paused.

Many customers, she said, “want to come into our place to experience what they’ve seen in a K-drama.” Orion Bar sells a lot of soju and imported Terra Lager, so she was particularly worried about higher prices on alcohol.

Eric Sze, the chef and an owner of the Taiwanese restaurants Wenwen and 886 in New York, was relieved this week by the hiatus on the 22 percent tariff on ingredients like sacha sauce and soy paste. These Taiwanese condiments are essential to dishes like 886’s sacha black-pepper beef, which help him to tell his customers about the country where he and his business partner grew up. “Food acts as the most accessible cultural ambassador,” he said.

Roscioli NYC, the SoHo outpost of a popular string of restaurants in Rome, has been worried about the cost of Italian wine, cheese and pasta, as well as the bottled sauces and preserved vegetables it sells.

“It’s impossible to imagine operating a restaurant without these products,” said Mattia Moliterni, the managing partner. “We don’t want to give up on that.”

Restaurants now have to wait to learn how far the prices of imported food and beverages will rise under the new 10 percent tariffs. And they are being left in suspense as they wonder when, or whether, the more severe rates will come back. Tariffs of any size are a shock to American restaurant culture, which has grown larger and more interesting in part because free-trade policies of the past few decades have made it possible to get almost anything from almost any country on earth.

“That’s been wonderful for chefs and also for consumers,” said Mr. Wrisley, the chef in Montana. “To take that away in the interest of reindustrializing the United States doesn’t make any sense.”

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The United States buys far more goods from China than China buys from the United States. But Beijing’s decision to retaliate against President Trump’s punishing tariffs by raising levies on American imports to 84 percent could sting more than Mr. Bessent let on.

“American companies that have been selling to China, and have been enormously successful doing that, are not going to be able to do that because of Chinese retaliation,” Sean Stein, the president of the U.S.-China Business Council, said in the hours before Mr. Trump ratcheted up his tariffs again.

“Tariffs on the Chinese side and the U.S. side cover everything,” Mr. Stein added, meaning everything from aviation to medical imaging to agriculture would be affected and “trade is going to slow,” he said.

The United States exported $143.5 billion of goods to China last year and imported $438.9 billion from that country, according to the Office of the United States Trade Representative.

The loss of China as an export market will deal a particularly hard economic blow to agricultural workers in many red states, hitting many of the voters who helped Mr. Trump win the presidential election. On Wednesday, Mr. Trump ratcheted U.S. tariffs on China even higher as he initiated a pause on “reciprocal” tariffs that he had imposed on other countries. The reprieve offers little relief for farmers who are concerned that a protracted trade war with China will cut off ties with their largest export market.

The first trade war with China, which lasted from 2018 to 2019, resulted in billions of dollars of lost revenue for American farmers. To help offset the losses, Mr. Trump handed out $23 billion in subsidies from a fund that the Department of Agriculture created to stabilize the farm sector. Large farm operations and farmers in the South benefited the most, fueling concerns about fairness and leaving some farmers feeling cheated.

The soybean industry is one of the sectors most concerned about the current tariff retaliation. China is America’s largest soybean export market, but when Mr. Trump imposed tariffs on Chinese goods during his first term, Beijing retaliated by buying soybeans from other countries, including Brazil.

“If this lasts long term, we’re going to have a significant number of farmers going out of business,” said Caleb Ragland, a Kentucky farmer who is president of the American Soybean Association. “We still bear scars from the last trade war.”

The American Soybean Association has been urging the Trump administration to strike a new trade deal with China to avoid a long-term trade war.

U.S. corn farmers, who sell about 2 percent of their products to China, have also been on edge about the trade fight. They welcomed Mr. Trump’s decision to pause punishing tariffs on other countries that could have led to more retaliation on farmers and other American businesses. But they urged the Trump administration to focus on negotiations that open up market access.

“The longer that uncertainty exists, the more concerned we become that our growers could harvest billions of bushels of corn for which they will not have reliable markets,” said Kenneth Hartman Jr., president of the National Corn Growers Association. “Our farmers want certainty that our customers at home and abroad will buy our products in the months and years ahead.”

Anxiety over the impact of the tariffs was evident on Wednesday as Jamieson Greer, the U.S. trade representative, testified before the House Ways and Means Committee and faced questions from Republicans who were nervous about retaliation from other countries against U.S. farm exports.

Representative Darin LaHood, a Republican from Illinois, said that he appreciated what Mr. Trump was doing to address longstanding trade barriers, but that his constituents were concerned.

“As I talk to my farmers, there’s a lot of anxiety, a lot of stress, a lot of uncertainty, because when we get into a trade war, usually the first pawn in the trade war is agriculture,” he said.

Mr. Greer responded that “almost all countries have announced that they’re not going to retaliate” except for China. Indonesia, India and many other countries “have affirmatively said we’re not retaliating,” he added, while some countries, like Vietnam, have unilaterally offered to lower tariffs on U.S. farm products. Mr. Greer did not mention that Europe announced retaliatory measures on Wednesday or that Canada had retaliated against previous rounds of tariffs.

Mr. Bessent downplayed the impact of China’s response on Wednesday morning, arguing on the Fox Business Network that the United States exports relatively little to China.

“China can raise their tariffs, but so what?” said Mr. Bessent, who owns as much as $25 million of North Dakota farmland that he must divest.

The retaliation could force the Trump administration to revive the bailouts to American farmers that were offered during the president’s first term.

Brooke Rollins, the agriculture secretary, said on Wednesday that such a relief package was being considered and that “everything is on the table.”

At a White House cabinet meeting on Thursday, Ms. Rollins noted that farmers and ranchers had been struggling because of inflation and were concerned about uncertainty over trade but that they supported Mr. Trump’s economic agenda.

“Your idea of using tariffs to ensure that we are putting forward and putting America first, no one understands that better than our farmers and our ranchers,” Ms. Rollins said. “The period of uncertainty that we’re in, they know that your vision will move us into an age of prosperity.”

Mr. Trump offered little clarity on Thursday about a truce with China, but the president expressed general optimism about the economic relationship.

Asked about the potential for a deal with China, Mr. Trump said he expected that “we’ll end up working out something that’s very good for both countries.”

The president initially hailed the trade deal that he reached with China during his first term as a success, but China ultimately failed to honor promises it had made to buy large quantities of American farm products. Meanwhile, almost all of the tariff proceeds the United States collected during that trade war were used to provide relief to the agriculture industry.

Farmers generally resist government handouts, but Mr. Ragland of the American Soybean Association said federal relief might be necessary in this case.

“If we continue to be used as a negotiating tool, and we’re going to be a sacrificial lamb on behalf of the bigger picture, we’re going to have to have an economic package to help us keep the lights on,” he said.

Tony Romm contributed reporting

Mr. Trump on Wednesday paused some of his tariffs, saying the markets were getting “yippy.” The U.S. government bond market is enormous and can influence moves in other assets around the world.

Yields on British government bonds, known as gilts, have jumped higher in recent days, particularly long-dated debt. The yield on the 30-year gilt soared to 5.58 percent on Wednesday, the highest since 1998.

Even as the yield came down somewhat on Thursday, the Bank of England said it would sell 750 million pounds, or $970 million, from its holdings of short-term bonds instead of longer-maturing ones “in light of recent market volatility.”

Since late 2022, the Bank of England has been selling bonds that it bought to bolster the economy during the 2008 financial crisis and the coronavirus pandemic. The plan got off to a rough start: It was delayed when the central bank stepped back in to buy bonds to halt the turmoil triggered when former Prime Minister Liz Truss proposed an aggressive tax-cutting budget that incited market chaos.

Andrew Bailey, the Bank of England governor, has previously said that there would be a “high bar” for changes to its plan for gilt sales outside of the regular annual review process.

The adjustment to the schedule on Thursday is an unusual move. The bank will sell the same amount of bonds. But by offloading short-term debt the pressure is reduced on long-term bonds — selling of those bonds by other investors has been the most intense and raised interest rates for government borrowing.

Long-dated gilt sales will be rescheduled for next quarter, the central bank said. It owns £621 billion in gilts, down from £875 billion at its peak in early 2022.

That is a drastic increase on a country that supplies much of what Americans buy. China is the second largest source of imports for the United States and the primary global manufacturer of cellphones, toys, computers and other products.

The 145 percent figure is also just a floor, not a ceiling. That amount is on top of other pre-existing levies that Mr. Trump already put in place including:

• 25 percent tariffs on steel, aluminum, cars and car parts

• Tariffs of up to 25 percent on certain Chinese goods that Mr. Trump imposed during his first term

• Tariffs of varying ranges on certain products in response to violating U.S. trade rules

The rapid changes in tariffs have caused significant confusion for importers, many of whom depend on Chinese products, including major retailers as well as small businesses. For an importer bringing in a container of products, the difference between a 125 percent tariff and a 145 percent tariff can amount to thousands of dollars.

The Trump administration has exempted goods that were already in transit from the new tariffs, meaning importers have not yet started to incur them. In the case of goods shipped by air, this will happen in the next few days, while goods moving by ship will take several weeks to arrive.

But behind those statements was a deep well of nervousness among Republican lawmakers who are hearing angst from their constituents and donors about the impact of Mr. Trump’s trade moves on the financial markets and the economy. Some of them have begun signing onto measures that would end the tariffs altogether or claw back Congress’s power to block the president from imposing such levies in the future.

“I’m just trying to figure out whose throat I get to choke if it’s wrong, and who I put up on a platform and thank them for the novel approach that was successful if they’re right,” Senator Thom Tillis, Republican of North Carolina, said of the sweeping tariffs on Tuesday during a hearing with Jamieson Greer, the Trump administration’s top trade official.

On Wednesday, after Mr. Trump pulled back most of the tariffs but retained a 10 percent tariff rate for most countries and announced additional penalties on China, Mr. Tillis still sounded anxious. He said the move was likely to “reduce some of the escalation,” but added that there was still considerable work to be done to prevent another market meltdown.

“We’ve got to get a deal before we get rid of uncertainty,” he told reporters soon after Mr. Trump announced the change in a social media post.

Senator Rand Paul of Kentucky, who has been among the most outspoken Republican critics of Mr. Trump’s tariffs, said he hoped the turnabout was a sign that someone was “talking some sense into the policy and being less extreme.”

“When you add a bunch of tariffs, you’ll lose $6 trillion in the marketplace,” Mr. Paul said on Wednesday. “When you get rid of the tariffs, guess what? It comes bounding back. Tariffs are perceived by millions of people as being bad for the economy, so I hope there’s a lesson learned.”

Mr. Paul has joined Democrats in cosponsoring resolutions that would end Mr. Trump’s tariffs, including one that passed the Senate last week to terminate the levies on Canada, which drew the support of three other Republicans.

In the House, Republican leaders have rushed to stymie such measures and insulate themselves from having to vote on the issue, at least until the fall. The maneuvers are a tacit acknowledgment that such votes would pose an impossible political dilemma: reject the tariffs and earn Mr. Trump’s ire or embrace them and risk the anger of their constituents.

For now, many of them are cheering Mr. Trump’s tariff pause.

“Behold the ‘Art of the Deal,’” Speaker Mike Johnson said in a statement lauding the president’s strategy. “President Trump has created leverage, brought many countries to the table and will deliver for American workers, American manufacturers and America’s future!”

If it was the plan all along, Republicans in Congress were kept in the dark. And despite the temporary reprieve, trade hearings on Capitol Hill this week demonstrated a degree of skepticism in the G.O.P. ranks that seemed unlikely to disappear.

During Tuesday’s hearing, Senator James Lankford, Republican of Oklahoma, who has opposed tariffs in the past and voted in favor of giving Congress more authority over tariffs during Mr. Trump’s first term, chided Mr. Greer for failing to outline a clear strategy for Mr. Trump’s levies, including how long they would remain in place.

“Everyone that I talked to is grateful that we’re actually attacking the trade deficit issue and trying to be able to bring down barriers to trade,” Mr. Lankford said. “They also want to get a timeline.”

A day later, Mr. Greer had been speaking with lawmakers in the House for several hours as markets continued to plummet when Mr. Trump announced his 90-day tariff pause.

Mr. Lankford said the shift would provide “tremendous” help to businesses in the short term, but suggested that the uncertainty would return soon after the initial relief faded.

“Obviously, three months from now there are still going to be some of these questions out there,” he said on Wednesday.

The skepticism reflects a fundamental disconnect between Mr. Trump and many Republican members of Congress who have spent decades promoting free trade and pushing back against the use of tariffs as a tool to promote effective trade relationships.

“I love President Trump — I’m his strongest supporter in the Senate,” Senator Ted Cruz, Republican of Texas, said on a podcast last week. “But here’s one thing to understand: A tariff is a tax, and it is a tax principally on American consumers.”

A group of Republican senators vented their concerns about the tariffs in an interview on Tuesday night on Sean Hannity’s program on Fox News, which Mr. Trump is known to watch routinely. And some are doing more than criticizing.

Last week, Senator Charles E. Grassley, Republican of Iowa, introduced legislation with Senator Maria Cantwell, Democrat of Washington, that would require the president to give Congress 48 hours’ notice of any new tariffs and require House and Senate approval within 60 days or they would automatically be canceled. A half-dozen Republican senators have signed on.

Even some Republican leaders have carefully calibrated their responses, deferring to Mr. Trump while making it clear they have concerns.

“There are a lot of very intricate trading relationships that exist today across the world,” said Senator John Thune, Republican of South Dakota and the majority leader, who has long praised trade deals that have resulted in lower tariffs that benefit farmers in his home state. “Ultimately, we don’t know what the economic impacts are going to be. We hope that the president is successful. And if he is and he gets some reciprocity from other countries around the world, you know this may all be temporary.”

With House Republicans shutting down any move to force a vote on Mr. Trump’s tariffs, it is unlikely that Congress will make any serious move to rein in his trade policies.

Senator Ron Johnson, Republican of Wisconsin, said Congress should reclaim its trade authority from the executive branch, but there was little chance of doing so given Mr. Trump’s inevitable veto and the lack of a two-thirds majority in each chamber to override it.

“I can’t really do anything about it now, so I want to give him the benefit of the doubt,” Mr. Johnson said of the president. “I’m hoping he succeeds. I’m not betting against him.”