Liz Cheney criticises the former president after losing to a Trump-backed candidate in Wyoming.
A leading Republican critic of Donald Trump has said the party “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 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 marked another victory for 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 repeated his false claims of election fraud in 2020 and defended him amid mounting legal troubles – have largely 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 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 – a 59-year-old lawyer who ran to be Wyoming governor in 2018 – was handpicked by the former president and has said she believed the election he ultimately lost to President Joe Biden was “rigged”.
In her victory speech, she said the result showed that Republicans will “hold our elected officials accountable for their actions” and “dislodge entrenched politicians”.
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.”