A leading Republican critic of Donald Trump says the party has "embraced his cult of personality" after she was ousted in a primary election.
Liz Cheney, 56, was defeated by the political newcomer and Trump-backed candidate Harriet Hageman in Wyoming.
She had faced an uphill battle to win re-election after joining the congressional committee investigating Mr Trump's attempts to cling to power.
Ms Cheney - once a rising star in the party - also voted to impeach Mr Trump.
The primary election in the broadly conservative state highlighted the competing wings of the Republican Party - with more traditional conservatives facing off against Trump-backed candidates around the country ahead of mid-term elections in November.
The result means Ms Cheney, a three-term congresswoman and the eldest daughter of former Vice-President Dick Cheney, will not contest her seat in the US House of Representatives which she has held since 2017.
It illustrated the continuing influence of Mr Trump, who has backed dozens of candidates ahead of the mid-term elections that will determine control of Congress as well as governorships and state legislatures.
And those candidates - who have mostly repeated his false claims of fraud in the 2020 presidential election and defended him amid mounting legal troubles - have performed well.
"I think the Republican Party today is in very bad shape," Ms Cheney told the Today programme on NBC. "The party... embraced Donald Trump [and] embraced his cult of personality."
Ms Cheney won her primary in 2020 by a wide margin, and she told the programme that she believed she would have been successful once again had she repeated Mr Trump's unfounded claims of voter fraud.
"That path would have required that I accept, that I embrace, that I perpetuate the Big Lie," she said.
Ms Hageman - who ran to be Wyoming governor in 2018 - was handpicked by the former president and has said she believes the election Mr Trump ultimately lost to President Joe Biden was "rigged".
In her victory speech, she said the primary result showed Republicans will "hold our elected officials accountable for their actions" and "dislodge entrenched politicians".
The 59-year-old spent decades as a trial lawyer, with a particular focus on defending the interests of the energy and mining sector while opposing environmental policies.
While she has since praised Mr Trump's record as president, Ms Hageman described the former president as "racist and xenophobic" before the 2016 election.
"[I] heard and believed the lies the Democrats and Liz Cheney's friends in the media were telling at the time," she told the New York Times last year.
Ms Cheney became a virtual outcast within her party over her criticism of Mr Trump. Only two of the 10 Republicans who voted to impeach him after his supporters attacked the US Capitol last year have successfully maintained their places on the ticket for re-election.
Speaking to Today, Ms Cheney said it was "dangerous" to elect officials who questioned the result of that election and described it as a "red line" that she would continue to resist.
"I am absolutely going to continue this battle," she said, before vowing to do "whatever it takes" to stop Mr Trump from returning to the White House.
There had been speculation in the lead-up to the primary that Ms Cheney was preparing to challenge Mr Trump for the Republican nomination in 2024. "[It] is something I'm thinking about and I'll make a decision in the coming months," she told Today.
Mr Trump earlier congratulated Ms Hageman on her victory in a post on his social media platform, Truth Social.
"Liz Cheney should be ashamed of herself, the way she acted, and her spiteful, sanctimonious words and actions towards others," he wrote. "Now she can finally disappear into the depths of political oblivion."
Elsewhere, Republican Sarah Palin - who is eyeing a political comeback - has advanced to November's election in Alaska in the race to represent the state in the House of Representatives.
She rose to prominence as a vice-presidential candidate in 2008, and Mr Trump is her key ally and supporter.
In the state's Senate race, Republican Senator Lisa Murkowski, 65, who has defied Mr Trump, is through to November's poll.
But under new voting rules one of her opponents will be another Republican, Trump-backed Kelly Tshibaka, 42.