Nan and William Nagle climbed into their Ford 150 pickup, buckled their seatbelts and said goodbye to the state they had called home for the past seven decades.

A removals firm had days before packed up the family home near Palo Alto where they had spent 35 years raising their children and riding horses in the sunshine.

As born-and-bred Californians the couple never imagined they would leave The Golden State, but as its progressive policies became more and more entrenched, they felt they had no choice.

So in May 2021 the Nagles and their two corgis, Freddie and Flossie, set off on the 20-hour journey to start a new life 1,200 miles away in “free” Montana.

“Leaving a home of 35 years is sad, but so much had changed over the years that the place we were leaving was very different, and not in a good way”, Mrs Nagle, 76, tells The Telegraph from the porch of her blue slatted house overlooking Whitefish Lake.

“It is rather bittersweet to see the destruction to a previously wonderful place and be forced to leave it behind.”

The Nagles are among scores of “political refugees” who have in recent years fled progressive blue states for Montana’s breathtaking natural beauty and conservative values.

And in a state where cows outnumber the population of 1.1 million by more than two-to-one, the influx of newcomers could have major national consequences and hand control of the Senate to the GOP.

A red wave has in recent years swept across Big Sky Country. Democrats have gone from holding six of the state’s eight statewide offices to just one clung onto by Senator Jon Tester, who is up for re-election on Nov 5.

The Democrats currently hold a 51-49 Senate majority and they are almost certain to lose Senator Joe Manchin’s West Virginia seat.

Whoever wins Montana, therefore, will likely control the Senate – and be able to stifle or wave through the sitting president’s ambitions.

A working dirt farmer who lost three fingers in a meat grinder at his family’s butcher shop when he was a child, Mr Tester has held onto his seat for 18 years by building a reputation as a moderate voice of rural America. His adverts show him driving his tractor and harvesting wheat on his family’s farm in Big Sandy.

Mr Tester has worked to distance himself from Kamala Harris and Washington – he hasn’t endorsed her and has refused to disclose whether he will vote for her. At his campaign office in Kalispell there are posters for a string of Democrat candidates – save for Harris/Walz.

This election is the first time Mr Tester, 68, has shared a ticket with Donald Trump and polls show him trailing his Republican rival Tim Sheehy, 38, a former Navy SEAL turned businessman who moved to Montana in 2014.

It is also taking place following a dramatic population boom in which families like the Nagles have descended on Montana.

Between 2020 and 2023, Montana’s population grew by 51,000, with California-born residents now making up more than seven per cent of the state’s population.

Mr Tester grasped his third term by a razor-thin margin of fewer than 18,000 votes in 2018.

Like the Nagles, lifelong Californian Nancy Irwin, a conservative, fled the blue state’s liberal politics for Montana.

“We felt like we had no voice”, she tells The Telegraph from a carpark in Kalispell, a city of around 30,000 people in the foothills of Glacier National Park, after attending one of Mr Sheehy’s rallies.

So in October 2020 she and her husband, who had spent their lives in Visalia, in the Central Valley, drove more than 1,200 miles to their recently purchased plot of six acres of land in Bigfork overlooking Swan Lake.

“We don’t have any relatives here, we didn’t know a soul here”, Mrs Irwin, who is in her early sixties, added.

Mrs Irwin, who works for the American Automobile Association, has already voted for Trump and Mr Sheehy. She resolved to become more politically active when she came to Montana and will be a judge on election day.

She “really hopes” transplants like her can tie up the Senate race for the Republicans.

Although Montana has not voted blue in the presidential election since Bill Clinton in 1992, the state was known for ticket-splitting to elect local Democrats.

Abhishek Chatterjee, associate professor and chairman of political science at the University of Montana, says the shift in the state’s politics to become solidly Republican has been a “new phenomenon” in the past five to six years.

“Montana is not like the Southern states. It has no history of just being what we would today in an American context, called conservative, it has no history of that.”

Don “K” Kaltschmidt, the Montana Republican Party chairman, is confident Mr Sheehy will win on Nov 5 after he witnessed the fortunes of statewide Republican candidates change from 2020.

“When we had Covid, when all these people moved in, we not only had slight majorities, but we had big majorities, because we won every race by as much as 20 points”, he tells The Telegraph.

“We got more and more people that were like minded to us… they fled from places like Washington state, Oregon state, California was the biggest one.

“We might have beat him [Tester] without the political refugees, but with the political refugees, it’s going to be a lot easier.”

Matt Regier, Republican Speaker of the Montana House of Representatives, agreed the state is “getting more red”.

“We’re getting the refugees, the people that don’t like the politics in their home state and are moving to places like Montana”, he says.

Among them is Janna Hipler, who when she was told she would have to take the Covid vaccine or lose her job at a hospital in Grand Rapids, Michigan, bundled her five-year-old son Aidan into the car and left.

“I Googled ‘Where won’t we have to wear a mask ever again?’”, said Ms Hipler, 38, who was also spurred to leave because of the Black Lives Matter protests.

“I was just like, no, like, with our riots and everything the BLM, he’s not being raised like this because it was causing stress”, she told The Telegraph between sips of her morning coffee.

They settled in Whitefish, some 1,800 miles away from Michigan, where Ms Hipler opened an age rejuvenation clinic.

She hasn’t decided who she is going to vote for in the election, but says she leans more conservative and wants to vote for a candidate who will protect personal freedom.

Another transplant, Lukas Schubert, 19, moved to Montana from Los Angeles with his mother in 2021 because of the restrictive Covid laws and liberal policies.

He is running to be a local Republican house representative, and if he wins he will become one of the youngest elected officials in the US.

“I’m getting involved in politics because I’ve personally experienced how bad it is in a place like California, we have Democrat trifecta, full Democrat control, and so I’m, you know, I am fighting to keep Montana, Montana”, he says.

But not everyone in Montana is thrilled about the arrival of droves of newcomers from the West Coast.

In Kalispell, which saw its population swell by 20 per cent from 2020 to 2023, cars drive around with bumper stickers in the shape of Montana state telling people to “get lost”.

The influx has also seen house prices increase by 70 per cent in five years, with a typical home costing $470,000 at the start of 2024, according to the state’s Labor Day Report.

Ms Hipler has had her fair share of abuse since moving and was harassed by a couple in a coffee shop in Kalispell when she was dressed in “New York style clothes”

“They were like: ‘You’re not from here’, I was like, ‘actually, I live in Whitefish’ and they said ‘that’s even worse’. People hate Whitefish, they call it California.

“People are driven off the road so I changed my licence plate right away,” she said.

With Pilates and Yoga studios stacked on top of trendy independent cafes serving avocado toast and an array of dairy-free milks, it is clear to see why some residents fear their new neighbours are changing things.

Fifth generation Montanan Donna Maddux, who lives in Whitefish, says the issue with newcomers arriving in Montana is they don’t have the right attitude.

”[They say] ‘Where’s my this?’ and ‘How do you provide that?’ and ‘How am I supposed to get this?’… We Montanans still have a kind of a pioneer attitude,” she says.

Mrs Maddux, who is part of 50 per cent of the state’s population who were born in Montana, didn’t disclose who she voted for, but described Mr Sheehy as “just plain arrogant”.

Byron, 28, who was born in Kalispell and cuts firewood for a living, was more direct .

“They can go back to where they came from, that’s how I feel about it, cos they’re jacking stuff up,” he says.

Speaking to The Telegraph as he tried to fix his broken-down truck filled with freshly lumbered wood, he adds:  “There’s a lot more I could say about Californians, I mean a lot, but I just won’t go there because it’s quite mean and definitely offend the snowflakes here.”

Eric Stern, a local Democrat strategist, still believes the Senate race is in play, but he admits the influx of newcomers isn’t going to make things easy.

“Democrats were dealing with pretty thin margins to begin with. It was always a challenge and this just makes it more challenging”, he says.

“Tester has beaten every opponent he’s ever faced for the past 18 years, and the Republicans’ last and final strategy, which may work, is to import Republican voters from other states.”

Back in Whitefish Mrs Nagle surveys the damage red potted geraniums caused by bears the night before. A few feet away, a row of placards for GOP candidates including Mr Sheehy are jammed into her lawn.

While she was in California she would have to use wire to tie down signs for Republicans to stop them being stolen, but in Montana, nobody has touched them.

The contrast is astonishing – she would “absolutely” describe herself as a political refugee.

“Even though some Montanans seem to resent Californians coming to the state, I think many newcomers are political refugees who will not try to turn Montana into California,” she tells The Telegraph.

“We are relieved to be out of a badly run state and away from the pervasive liberal attitude”, she adds.

Whether she and other Republican newcomers will help tip the balance to unseat Montana’s last statewide Democrat remains to be seen.