Republican dissident Liz Cheney looks set to lose her US Congress seat Tuesday to an election-denying conspiracy theorist, in the latest signal of her party's disavowal of traditional conservatism in favor of Donald Trump's hardline "America First" movement.

Once considered Republican royalty, the lawmaker from Wyoming has become a pariah in the party over her role on the congressional panel pursuing Trump over the plot to overthrow the last election that culminated in the 2021 assault on the US Capitol.

All eyes are on the Wyoming Republican primary, where defeat for the 56-year-old elder daughter of Republican grandee and former vice president Dick Cheney would mark the end of the family's four-decade political association with one of America's most conservative states.

Even her loyal backers have privately accepted that Cheney will likely lose to 59-year-old lawyer Harriet Hageman -- Trump's hand-picked candidate who has amplified his false claims of a "rigged" 2020 election.

The latest survey from the local Casper Star-Tribune has Cheney with just 30 percent support compared with 52 percent for Hageman, reflecting all recent polling.

Yet there is already speculation that Cheney may challenge Trump for the Republican presidential nomination in 2024 -- or even run as an independent -- and insiders are expecting her to deliver a concession speech that will double up as the launchpad for her political future.

"No matter how long we must fight, this is a battle we will win. Millions of Americans across our nation -- Republicans, Democrats, independents -- stand united in the cause of freedom," she said in a video message posted before the weekend.

"We are stronger, more dedicated and more determined than those trying to destroy our republic. This is our great task and we will prevail."

Cheney has framed her campaign as a battle for the soul of a party she is trying to save from the anticonstitutional forces of Trumpism, but it is far from clear that the feeling is mutual.

She is the last of 10 House Republicans who backed the former president's second impeachment to be facing primary voters.

Four retired rather than seek reelection, three lost to Trump-backed opponents, and only two -- California's David Valadao and Dan Newhouse of Washington state -- have made it through to November's midterm elections.

More than 70 percent of Wyoming voters cast their ballot for Trump in the last presidential election against Joe Biden.

Cheney voted in line with Trump's positions 93 percent of the time when he was president but that hasn't blunted his retaliation for her role in the House committee probe.

Trump has made Cheney his bete noire, calling her "disloyal" and a "warmonger."

The blonde, bespectacled former attorney has been made persona non grata by the Wyoming Republican Party, whose chairman himself participated in the protests on the day of the US Capitol assault.

In her state, the first to grant women the right to vote, in 1869, the congresswoman has been forced to run a kind of shadow campaign, with no election rallies or public events.

Her part in investigations into Trump and his entourage have prompted death threats and she now travels with a police escort.

"Liz is representing the constituents that are in her mind, and they aren't the constituents of Wyoming," said Mary Martin, chairwoman of the Republican Party in Teton County -- Cheney's Wyoming base.

Leaning on his red motorcycle, Bill Gonzales, 59, is one of the few voters who spoke to AFP in Cheyenne to defend Cheney's record, saying she "has stood up for what is proper within the country."

"We live in the United States of America. And our elections are secure. Our elections are fair. And anybody who says they're not is lying, plain and simple," said the local government official, who is a registered Republican and a lifelong Cheyenne resident.

"If Ms. Cheney wins, I guarantee you a number of people are going to say the election is rigged," he went on.

"And no, it's not."