During a call with President Volodymyr Zelensky of Ukraine this week, President Trump floated a highly unusual idea: The United States could take control of Ukrainian nuclear power plants.

“The United States could be very helpful in running those plants with its electricity and utility expertise,” the White House said in a statement after the call on Wednesday. “American ownership of those plants would be the best protection for that infrastructure and support for Ukrainian energy infrastructure.”

The idea surprised officials and energy experts in Kyiv, and it was not clear whether Mr. Zelensky would agree to such a plan. Ukraine owns four nuclear power plants, and it also appears that the two sides do not agree on how many facilities the idea concerns.

Mr. Zelensky suggested at a news conference that the idea was limited to the Zaporizhzhia nuclear power plant, Europe’s largest, which is now under Russian control.

The Ukrainian leader described his discussions with Mr. Trump about the plant as “positive steps,” but added, “I’m not sure we will get a result quickly.”

The White House statement echoed a familiar argument from Mr. Trump: that U.S. economic involvement in Ukraine serves as its best security guarantee, because Russia would be less likely to target a country where America has economic interests. Mr. Trump has also applied such reasoning to a potential deal on access to Ukrainian critical minerals.

So what could the United States’ interests be in Ukraine’s nuclear sector, and what challenges might it face?

U.S. Economic Interests

Ukraine’s Soviet-era nuclear power plants have been the backbone of its energy network during the war, supplying up to two-thirds of the country’s electricity. While Moscow has relentlessly attacked Ukraine’s thermal and hydroelectric power plants in an effort to cripple its grid, it has avoided striking nuclear facilities, which could trigger a radiological disaster.

Against that background, the Ukrainian government has initiated plans to build more nuclear reactors, arguing that it is the only viable solution to ensuring long-term energy security.

This is where America’s business interests could come into play.

Shortly before the war, Westinghouse, an American nuclear technology company, signed a deal with Energoatom, Ukraine’s state-owned nuclear company, to build five reactors. After Russia attacked, the number was increased to nine and the two companies agreed to further cooperate to deploy smaller plants in Ukraine.

For Westinghouse, it was a breakthrough after years of struggling to enter a Ukrainian nuclear market long dominated by Rosatom, the Russian nuclear power giant.

Westinghouse has a special interest in the six-reactor Zaporizhzhia nuclear plant. Russia captured the plant in March 2022, and it no longer supplies electricity to the Ukrainian grid. But before the war, it used fuel and technology from Westinghouse.

Olga Kosharna, a Ukrainian nuclear safety expert, said that Russia’s capture of the Zaporizhzhia plant had raised concerns at Westinghouse about the potential theft of its intellectual property. In 2023, the U.S. Energy Department warned in a letter to Rosatom that the company could face prosecution under U.S. law if it used Westinghouse technology at the plant.

Andrian Prokip, an energy expert with the Kennan Institute in Washington, said that Westinghouse would “definitely benefit” from a return of the plant to Ukrainian hands, as it would expand its market.

It is unclear whether Mr. Trump discussed the fate of the Zaporizhzhia plant with President Vladimir V. Putin of Russia in a call on Tuesday as he had vowed to.

Westinghouse did not immediately respond to a request for comment.

A current Ukrainian official and a former one, both with knowledge of the talks between the United States and Ukraine, also said Kyiv had emphasized to Mr. Trump that if the United States wanted access to Ukrainian minerals, it would require the Zaporizhzhia plant’s power-generating capacity, because mineral extraction and processing is energy intensive.

Possible Challenges

For one thing, all of Ukraine’s nuclear power plants are owned by Energoatom, and Ukrainian law prohibits their privatization.

Amending Ukraine’s laws to allow for U.S. ownership would be politically sensitive in a post-Soviet country where many key industries remain state-owned.

Ukraine has engaged in a wave of privatization during the war. But privatizing Energoatom — the state-owned company that generates the most revenue — would likely be a sticking point.

“I expect there would be great resistance to this idea in Ukraine,” said Victoria Voytsitska, a former Ukrainian lawmaker and senior member of Parliament’s energy committee. “From both sides of the political spectrum.”

Mr. Zelensky alluded to the issue in his news conference after his call with Mr. Trump. If Russia returned the Zaporizhzhia plant to Ukraine — a prospect that many in Ukraine deem unlikely — “simply handing over the plant” to the United States would not be possible, Mr. Zelensky said, because “it’s ours and it’s our land.”

Making plants operational again after three years of war would also pose a considerable challenge. Mr. Zelensky cited a period of up to two and a half years to get the degraded Zaporizhzhia plant running again.

Further, although all six Zaporizhzhia reactors have been shut down, they still require energy to power critical safety systems and water to circulate in their cores to prevent a meltdown.

But the power lines providing power to the plant have been cut on several occasions in the war, and the destruction of a nearby dam, possibly at Russia’s direction, has reduced access to cooling water, raising the risks of a nuclear accident.

Prime Minister Benjamin Netanyahu of Israel was expected on Thursday to formally fire the head of the Shin Bet domestic intelligence agency, despite growing street protests and scuffles over the move that have further roiled a deeply divided country still at war.

The Israeli cabinet was set to convene for a nighttime vote on the dismissal of the Shin Bet chief, Ronen Bar, just days after Mr. Netanyahu announced his intention to oust him, citing a lack of personal trust between them.

It comes after Israel’s military resumed a deadly campaign in Gaza that has raised concern among many Israelis about the fates of hostages still held in the enclave. Sirens warning of incoming rocket fire from Gaza sent Israelis in the Tel Aviv area running for cover on Thursday for the first time in months.

The Shin Bet is deeply involved in Israel’s war against Hamas in Gaza, providing intelligence and targets. By law, the agency is also tasked with protecting Israeli democracy.

The discord between Mr. Netanyahu and Mr. Bar goes to the heart of a broader battle playing out over the nature and future of Israel’s democracy and the rule of law. Critics of Mr. Netanyahu’s ruling coalition, the most right-wing and religiously conservative in Israel’s history, accuse it of working to reduce the authority of independent state watchdogs and to remove checks and balances on the powers of the government, which holds a narrow majority in Parliament.

The firing of Mr. Bar on grounds of personal trust has also raised public concerns that future appointments may be based primarily on loyalty to the prime minister.

Thousands protested in Jerusalem on Wednesday in anticipation of the move, and more protests took place on Thursday. By lunchtime, a long column of academics had marched in stormy weather from a campus of the Hebrew University of Jerusalem toward one of Mr. Netanyahu’s private residences, beating on drums, chanting, “Democracy!” and scuffling with police officers after trying to break through a barricade.

Some prominent opposition figures joined the demonstrators. Video footage from the scene showed police officers aggressively pushing protesters, including Yair Golan, a former deputy chief of the military and now the leader of the center-left Democrats party, who ended up on the ground. The police used a water cannon and sprayed protesters with a foul-smelling liquid in an effort to disperse them.

The new protests recall weekly demonstrations in 2023 against attempts to overhaul the judiciary to reduce its power as a check on the government, with business leaders at one point joining labor unions to hold a national strike. Those protests came to an abrupt halt with the Hamas-led attack on southern Israel that ignited the war on Oct. 7, 2023, though the broad sense of national solidarity that prevailed then is now fraying.

Mr. Netanyahu and his allies have made accusations of overreach against the judiciary and other independent branches, saying that they have hampered the government’s freedom to make decisions and to represent the will of voters.

Mr. Netanyahu has been under police investigation and is on trial on charges of corruption, which he denies. He has repeatedly accused a liberal “deep state” of conducting a witch hunt against him and his family.

For months, Mr. Bar had angered Mr. Netanyahu by investigating officials in the prime minister’s office over claims that they had leaked secret documents to the media and also worked for people connected to Qatar, an Arab state close to Hamas. The investigation, called “Qatargate” in the local news media, is continuing in secrecy under a sweeping gag order.

Mr. Netanyahu has denied wrongdoing and his office has dismissed the episode as “fake news.” The Qatari government did not respond to requests for comment.

Mr. Bar, who has led the Shin Bet since 2021, issued a rare public statement last week, after Mr. Netanyahu’s announcement, saying that the expectation of “personal trust” was in opposition to the public interest.

“It’s a fundamentally flawed expectation that is in contravention with the Shin Bet law and statesmanship,” Mr. Bar said.

Mr. Bar and the Shin Bet have taken responsibility for their part in the intelligence failure that led to the Hamas-led attack, which resulted in the deadliest single day for Israelis since the foundation of their state in 1948.

But in a summary of the agency’s internal probe into its conduct issued earlier this month, the Shin Bet also pointed to years of lenient government policy toward Hamas and Gaza as a major contributing factor, likely angering Mr. Netanyahu.

Appearing emboldened domestically, as well as in Gaza, by the staunch support of the U.S. administration, Mr. Netanyahu made common cause with President Trump in a blunt social media post late Wednesday.

“In America and in Israel, when a strong right wing leader wins an election, the leftist Deep State weaponizes the justice system to thwart the people’s will,” he wrote. “They won’t win in either place! We stand strong together.”

The billionaire Elon Musk, a close ally of Mr. Trump, replied with a red “100” emoji, suggesting that he agreed with Mr. Netanyahu.

Many Israelis view the country’s democracy as increasingly fragile. Israel has no formal written constitution, only one legislative chamber and a president whose role is mostly ceremonial and symbolic.

By taking the vote straight to the government on Thursday, Mr. Netanyahu was also defying a legal opinion of the attorney general, Gali Baharav-Miara, who advised that the dismissal of Mr. Bar must first be approved by an advisory committee that oversees senior appointments.

Ms. Baharav-Miara, who was appointed by the previous government, has frequently clashed with the current one. Prominent members of Mr. Netanyahu’s cabinet have said that after Mr. Bar’s removal, the attorney general will be the next.

The families of hostages still held in Gaza, up to 24 of whom are believed to be alive, have expressed outrage and alarm over what they view as Mr. Netanyahu’s misguided priorities, as well as the collapse of a temporary cease-fire and the renewed military campaign.

“First, return the hostages. Everything else comes after!” the Hostages and Missing Families Forum, a grass-roots organization that advocates on behalf of captives and their relatives, said in a statement on Thursday. The forum described the hostages as being “in danger of death and disappearance in the Hamas tunnels in Gaza.”

Myra Noveck in Jerusalem and Rawan Sheikh Ahmad in Haifa, Israel, contributed reporting.

Prime Minister Viktor Orban of Hungary pioneered many of the themes dear to conservatives in the United States, railing for years against “migration insanity,” “the woke virus” and “gender madness.”

Now Mr. Orban is engaged in an effort that veers away from the orthodox conservative view that the state should stay out of the economy. He’s trying to set the price of eggs and other goods.

Unable to curb Hungary’s inflation rate, the highest in the European Union, and facing a surge of support for a political rival, Mr. Orban last week ordered price controls on 30 basic foodstuffs. And he accused supermarkets of price gouging, particularly on eggs and butter.

Mr. Orban said the Hungarian government would starting this week force supermarkets to bring down their prices by ensuring that what they charge for essential foods does not exceed a 10 percent markup on what they cost wholesale. The current markup for eggs, he said, was an “unacceptable” 40 percent.

“Prices don’t rise, they are raised,” Mr. Orban thundered, blaming inflation on grocery stores, the biggest of which in Hungary are foreign companies like Britain’s Tesco and Austria’s Spar.

Hungary has been hailed by many American conservatives (and President Trump) as a beacon for how a country should be run. But the move by Mr. Orban underlines how he has struggled to manage the thing many Hungarians care about most: their country’s ailing economy.

Economic troubles have weakened Mr. Orban at home and abroad. The Hungarian Economic Research Institute, an independent body, reported recently that its business confidence index had “slipped to a 50-month low.”

Those troubles have badly dented Mr. Orban’s popularity ahead of an election next year that, according to some opinion polls, his governing Fidesz party could lose to an upstart opposition movement led by Peter Magyar, a former party loyalist.

Mr. Magyar has rocketed to national fame as the leader of a mass movement built on denunciations of Mr. Orban over Hungary’s “staggering cost-of-living crisis,” its faltering public services and an economic playing field tilted in favor of businesses controlled by the prime minister’s relatives and political allies.

In Budapest on Saturday, Mr. Magyar drew tens of thousands of anti-government protesters to a rally commemorating Hungary’s failed 1848 revolution, far more than attended a similar event held earlier in the day by Mr. Orban.

Mr. Magyar mocked Marton Nagy, the economy minister, for trying to dictate the price of sour cream, a Hungarian staple, by “circling numbers with a ballpoint pen to see how much the price can be cut” while Mr. Orban, his family and friends “become rich stealing your money.” The crowd roared.

Erika Lapos, a retiree who traveled more than 100 miles with her husband from their home in northeastern Hungary to attend Mr. Magyar’s rally, blamed corruption for the weak economy. “Is not just a scandal, it is a crime,” she said.

Mr. Orban had until recently largely succeeded in deflecting criticism of his economic record and corruption by blaming high prices on the war in Ukraine. He also sought to focus public attention on issues like illegal immigration and his false accusations that the European Union was trying to turn Hungarian children transgender or gay.

But the Ukraine war and migration no longer dominate voters’ concerns, said Agoston Mraz, director of the Nezopont Institute, which conducts polls for Mr. Orban’s government.

“The inflation issue is now the most important by far,” he said.

Still, eager to change the topic and rev up Mr. Orban’s conservative base, his supporters in Parliament on Tuesday amended a law on public assembly to ban gay pride parades, the latest in a series of efforts to target the country’s L.G.B.T.Q. community.

But there’s no escaping the economic realities.

Overall, Hungarian food prices in February, according to official figures released last week, were 7.1 percent higher than a year earlier, meaning that food is now more than 80 percent dearer than five years ago, according to calculations by ING Bank.

Mr. Mraz said that, according to his institute’s polling, Fidesz still had a solid lead over Mr. Magyar’s Tisza party but was vulnerable on the economy.

Economic woes have also weakened Hungary’s hand in its long struggle with the European Union over sanctions on Russia — Mr. Orban wants them removed — and a host of other issues relating to the rule of law, democracy and corruption.

Short of cash to fill a big hole in its budget, Hungary has no real chance of getting financial aid from Mr. Trump, despite their close political ties, and increasingly needs money from the European Union, which has frozen more than $20 billion earmarked for it years ago.

In a blunt warning to Mr. Orban, who has infuriated European leaders by constantly vilifying them, the European Union’s executive arm on Dec. 31 took about 1 billion euros, or about $1.1 billion, of Hungary’s frozen money off the table, saying a time limit had expired.

On Friday, after weeks of attacks on the bloc by Mr. Orban as an “empire” of “warmongers” before which his country would never bow, Hungary quietly sheathed its veto power and agreed to allow the renewal of European sanctions imposed on more than 2,400 mostly Russian individuals and entities.

Mr. Orban’s jeremiads against Brussels, said Zoltan Pogatsa, an economics professor at the University of West Hungary, play well with his nationalist political base but “don’t help pay the bills.”

Before the European Union froze the bulk of its funding, he added, “money from Brussels drove most of the growth during what Mr. Orban calls the golden years,” a period of high growth and relatively stable prices during his first decade in power before the Covid pandemic.

After slipping into recession last year, Hungary’s economy is growing again, albeit at a very slow pace. But investment, a key driver of future growth, has plummeted, Mr. Pogatsa said. And the hole in the budget — a gap criticized by the European Union last month as an “excessive deficit situation” — is likely to balloon if, as he did before the last election in 2022, Mr. Orban offers handouts to voters before the one next year.

Mr. Orban last month announced what he described as the “biggest tax reduction program in Europe,” promising to exempt mothers with two or more children from income tax and give pensioners a rebate on the value-added tax they pay on foodstuffs.

At 27 percent, Hungary has the highest such tax in the European Union, and many economists say the easiest way to reduce food prices would be to reduce it, and also a special 4.5 percent tax on retailers.

But doing that would increase the budget deficit at a time when neither the European Union nor the United States is offering cash.

The ratings agency Standard & Poor said in November that it had downgraded its outlook for Hungary to negative, largely because it “may ultimately lose out on a substantial amount of the envisaged European Union funds.”

“No matter how much anti-E.U. rhetoric he uses, Orban realizes that he still has to squeeze some juice out of Brussels,” said Lajos Bokros, a former finance minister.

He said Mr. Orban viewed inflation and other problems entirely through a political lens. “His government created inflation with its loose spending,” he said, “but lies to voters that it was imported from outside” — by supermarket chains, most of which are foreign-owned, and by higher energy prices because of the war in Ukraine.

Sensing political danger ahead, Mr. Orban responded swiftly to the release of official data showing that Hungary’s year-on-year inflation rate had risen in February to 5.6 percent.

“We will put an end to excessive and unjustified price increases,” he said. He did not specify how this would be done, but Hungary’s state statistics office on Wednesday said that Mr. Orban’s intervention had already lowered egg prices by nearly 20 percent.

Geza Sebestyen, the head of the Center for Economic Policy at Mathias Corvinus Collegium, a conservative government-affiliated university, said Mr. Orban was unlikely to send inspectors to punish shopkeepers who hadn’t lowered prices. “Socialism obviously doesn’t work,” he said, “and Eastern Europe knows that better than anyone.”

But Peter Bod, a former governor of Hungary’s central bank, fears Mr. Orban is reaching for communist-era tools in what is supposed to be a free market.

“Instead of goulash communism,” he said, referring to the country’s idiosyncratic reworking of Soviet-imposed socialism in the 1960s and ’70s, “we got goulash capitalism.”

Barnabas Heincz contributed reporting.

Hamas fired its first barrage of rockets in months into Israeli territory on Thursday as Israeli troops expanded their ground raids in northern Gaza in what looked increasingly like a slide back into full-scale war.

There were no reports of casualties from the rockets, which were fired at Tel Aviv. The Israeli military said they were either intercepted or fell in open areas. But the barrage served as a show of resilience from the Palestinian armed group despite more than a year of war with Israel.

A two-month cease-fire collapsed this week with an Israeli aerial bombardment of Gaza, which the military said had targeted Hamas. Israel argued that the truce could not continue unless Hamas released more hostages, while Hamas accused Israel of violating the cease-fire agreement.

Israel’s renewed assault has killed more than 500 people in Gaza in three days, including scores of children, the Gaza health ministry said on Thursday. Those figures do not distinguish between civilians and combatants.

Earlier on Thursday, the Israeli military said its forces had begun conducting “ground activity” near Beit Lahia, in northern Gaza. That came less than a day after Israel announced that it had recaptured part of the Netzarim corridor in central Gaza, which divides the north of the territory from the south. Israel had withdrawn from the corridor as part of the truce.

Hamas said at least five of its top leaders in Gaza were among about 400 people killed by Israel on Tuesday in a heavy bombardment, according to Gaza officials. Hamas rarely provides information as to whether those killed in Israeli attacks were members of the armed group.

Benjamin Netanyahu, the Israeli prime minister, has vowed to step up pressure on Hamas until the group capitulates and releases the dozens of Israeli and foreign hostages still being held in Gaza.

Hamas officials say Israel will not gain more favorable terms for a cease-fire by resuming the war.

The first phase of the January cease-fire ended in early March. Mediators like the United States were trying to broker a deal between Israel and Hamas on the next steps in the truce, including a permanent end to the war and the release of the remaining living hostages in Gaza.

But Israel has been unwilling to end the conflict permanently as long as Hamas remains in power in Gaza. Hamas is refusing to disband its armed battalions, send its leaders in Gaza into exile or release many more hostages unless Israel commits to a permanent end to the war.

About 24 living Israeli and foreign hostages — as well as the remains of more than 30 others — are believed to still be in Gaza, according to the Israeli government.

Hamas and its allies abducted about 250 people during the Oct. 7, 2023, attack on Israel that ignited the war.

A French scientist was prevented from entering the United States this month because of an opinion he expressed about the Trump administration’s policies on academic research, according to the French government.

Philippe Baptiste, France’s minister for higher education and research, described the move as worrying.

“Freedom of opinion, free research and academic freedom are values we will continue to proudly uphold,” Mr. Baptiste said in a statement. “I will defend the possibility for all French researchers to be faithful to them, in compliance with the law, wherever they may be in the world.”

Mr. Baptiste did not identify the scientist who was turned away but said that the academic was working for France’s publicly funded National Center for Scientific Research and had been traveling to a conference near Houston when border officials stopped him.

The U.S. authorities denied entry to the scientist and then deported him because his phone contained message exchanges with colleagues and friends in which he expressed his “personal opinion” on the Trump administration’s science policies, Mr. Baptiste said.

It was not immediately clear what led the border authorities to stop the scientist, why they examined the contents of his phone or what they found objectionable about the conversations.

Customs officers are allowed to search the cellphone, computer, camera or any other electronic device of any travelers crossing the border, according to U.S. Customs and Border Protection, although the agency says that such instances are rare. In 2024, less than 0.01 percent of arriving international travelers had their electronic devices searched, according to the agency.

Mr. Baptiste’s office declined to provide further details about the case, and the National Center for Scientific Research did not immediately respond to a request for comment. A spokesman for the American Embassy in Paris declined to comment.

The Agence France-Presse news agency reported earlier on the scientist’s refused entry to the United States.

Mr. Baptiste has been particularly vocal over the past few weeks in denouncing threats to academic freedom in the United States, where funding cuts and layoffs by the Trump administration have targeted institutions of higher education, scientific research and the federal government’s own scientific work force.

Mr. Baptiste has also urged French universities and research institutes to welcome researchers seeking to leave the United States.

“Europe must be there to protect research and welcome the talent that can contribute to its success,” Mr. Baptiste wrote on social media after meeting with his European counterparts in Warsaw on Wednesday to address “threats to free research in the United States.”

Ségolène Le Stradic contributed reporting.

Officials from the European Union said on Thursday that they would delay their retaliation against President Trump’s steel and aluminum tariffs — including 50 percent levies on American whiskey and other goods — until the middle of next month.

The move is meant to give officials time to refine the list of products that will be hit while also allowing more time to strike a deal with the United States, said Olof Gill, a spokesman. The first wave of E.U. tariffs were originally set to kick in on March 31, with a second wave coming a few weeks later.

The postponement could allow officials to reconsider whether they want to impose such big tariffs on sensitive products like bourbon. And it comes as Europe tries to prevent its trading relationship with the United States — arguably the globe’s most important — from devolving into a tit-for-tat trade war that costs consumers and companies on both sides of the Atlantic.

“The E.U. and the U.S. enjoy the largest bilateral trade and investment relationship in the world,” Maros Sefcovic, the bloc’s trade commissioner, said during a speech in Brussels on Thursday. “It should be a priority for both sides to protect and further develop this relationship.”

Mr. Sefcovic, who is in charge of negotiating trade matters for the E.U., talked to his American counterparts by phone last week. He said on Thursday that he had learned that the Trump administration did not want to negotiate on trade until after April 2, when the United States is expected to announce a new and even more sweeping round of tariffs on its global trading partners.

“For them, this should serve as a base line for redefining and rebuilding U.S. trading relations with the rest of the world,” Mr. Sefcovic said. “Only then may partners be able to engage on possible negotiations.”

The delay in negotiation has complicated the original start date for Europe’s retaliatory tariffs, which E.U. policymakers had always hoped would be a tool to prod the Americans to the negotiating table.

The E.U. announced its tariff package last week in response to steel and aluminum tariffs that began on March 12. The European plan was originally meant to take effect over two phases.

The first — the one that is now delayed — would have allowed a set of tariffs that had been instituted during Mr. Trump’s first presidency and then suspended during the Biden administration to snap back into place at higher levels. Whiskey, motorcycles and a range of other products would have been affected.

The second phase would have placed new tariffs on a wide array of American products. Member states were meant to consult on the proposed list, set out in a 99-page document covering everything from lingerie to soy products to machinery parts. Those tariffs were set to begin in mid-April.

Now, all of the tariffs are expected to take hold next month, adding heftier levies on up to 26 billion euros, about $28 billion, worth of exports.

Slowing down the process could allow officials more time to take feedback into account and make edits, relevant at a moment when the continent’s plan has already met with a prompt and painful response from Washington.

Mr. Trump said he would impose a crushing 200 percent tariff on European champagne, wine and other alcohol to retaliate against Europe’s plan to hit American whiskey in particular.

That threat has stoked alarm among European leaders from wine-producing nations. Giorgia Meloni, Italy’s prime minister, has warned against a “vicious circle” of trade measures, and François Bayrou, the prime minister of France, has said Europe is at risk of “hitting the wrong targets.”

Whiskey was originally placed on the tariff list during Mr. Trump’s first trade war, in 2018, as a way to target Senator Mitch McConnell, Republican of Kentucky, who was then the majority leader. Bourbon is an important export from his home state. But with a new crop of leaders in Congress and surrounding Mr. Trump, the political calculus around such products has shifted.

Hanging over everything is what more might happen before mid-April.

While details on the new tariffs that the United States might impose on April 2 remain scant, Europe has been bracing for their impact. Mr. Trump has at times threatened that levies on cars and other products could be as high as 25 percent — a painful blow to German automakers, for instance.

Mr. Sefcovic said on Thursday that the United States could also unleash further trade measures on copper, wood and shipbuilders.

Christine Lagarde, the president of the European Central Bank, suggested on Thursday that tariffs were being used as “blackmail,” and that they could both sharply reduce European growth and add uncertainty to the outlook for price inflation.

But she said that if the E.U. responded by striking closer trade deals both internally and with other trading partners, it could offset those potential consequences.

“The answer to the current shift in U.S. trade policies should be more, not less, trade integration, both with trade partners around the globe and within the E.U.,” Ms. Lagarde said.