Liz Cheney, Donald Trump's fiercest Republican critic in Congress, has lost her seat in a major victory for the former president, but vowed to do everything she could to keep him from returning to the White House.
Ms Cheney, who had framed herself as a defender of American democracy, was soundly defeated in Wyoming's GOP primary by a Trump-backed challenger, Harriet Hageman, on Tuesday night.
She will now be forced from Congress at the end of her term in January.
But in a highly charged concession speech, she invoked Abraham Lincoln as she described her loss as the "beginning of the battle" and hinted she may challenge Mr Trump in 2024.
"Now the real work begins," she told a group of supporters including her father, the former US Vice President Dick Cheney, on the edge of a vast field in Jackson, Wyoming.
"Two years ago, I won this primary with 73 per cent of the vote. I could easily have done the same again," she said. "But it would have required that I go along with President Trump's lie about the 2020 election."
"I have said since Jan 6 that I will do whatever it takes to ensure Donald Trump is never again anywhere near the Oval Office - and I mean it."
She went on to allude to higher political ambitions, telling the crowd: "Lincoln was defeated in elections for the Senate and House before he won the most important election of all."
The three-term congresswoman has become a figurehead for Republican opposition to Mr Trump, and was a driving force behind the Congressional investigation into his role in last year's January 6 deadly attack on the US Capitol. She had halted in-person campaign events earlier in the year after receiving several death threats.
Her vocal criticism of Mr Trump had made her one of the former president's most high-profile targets in his crusade to purge the GOP of his critics.
Mr Trump called her defeat "a complete rebuke" of the congressional January 6 Committee. "Liz Cheney should be ashamed of herself, the way she acted, and her spiteful, sanctimonious words and actions towards others," he wrote on his social media platform. "Now she can finally disappear into the depths of political oblivion where, I am sure, she will be much happier than she is right now. Thank you Wyoming!"
The former president's supporters gleefully welcomed news of Ms Cheney's defeat. His son, Donald Trump Jr, tweeted: "Bye bye Liz Cheney" alongside a video montage of his father fist bumping and dancing.
Ms Cheney's primary race represents the last of the 10 Republicans in the House of Representatives who voted to impeach Mr Trump over his role in the January 6 attack, when a mob of his supporters attempted to stop the certification of Joe Biden's victory in Congress.
Mr Trump has backed Republican challengers who have repeated his disputed claim the 2020 election was stolen in races across the country, a largely effective campaign which has dealt a body blow to the moderate wing of the Republican party establishment.
With more than 70 per cent of the vote counted, Ms Hageman, a prominent lawyer in Wyoming, led Ms Cheney with 65 per cent to 31 per cent in the state's primary.
The defeat of Ms Cheney, once the third-ranking Republican in the House of Representatives, would have been unthinkable just two years ago in Wyoming, a deep red state where the Cheney name has long been synonymous with political power.
Her defeat is just the latest sign of the evolution of the Republican Party under Mr Trump.
Four-hundred miles to the east, festive Hageman supporters gathered at a sprawling outdoor rodeo and Western culture festival in Cheyenne, many wearing cowboy boots, hats and blue jeans.
"Obviously we're all very grateful to President Trump, who recognises that Wyoming has only one congressional representative and we have to make it count," Ms Hageman said.
Ms Hageman, a ranching industry attorney, once again repeated Mr Trump's unsubstantiated claims the 2020 election was "rigged" as she courted his base.
Mr Trump also looms large over two high-profile races in Alaska, where Republican senator Lisa Murkowski faces Trump-backed rival Kelly Tshibaka, and where former vice-presidential candidate Sarah Palin is vying to take the state's sole seat in Congress with his backing. Ms Cheney's defeat was on the minds of Republican voters campaigning for Ms Murkowski on the streets of Anchorage on Tuesday night.
Branch Haymans, a 61-year-old financial adviser, who stood outside a polling station in the city, said the defeat of a "strong conservative" like Ms Cheney was "disturbing".
"I'm worried about the bigger trend of people becoming so negative and divisive. I've been a registered Republican since 1978. I don't recognise the Republican Party anymore," he told The Telegraph.
The Lincoln Project, an anti-Trump conservative group, said: “Tonight, the nation marks the end of the Republican party."
John Bolton, Mr Trump's former national security adviser, said Ms Cheney’s loss "diminishes our party".
"By putting her Constitutional responsibilities above partisanship and political future she deserves the highest possible praise," he said.