Former President Donald Trump poses a "domestic threat" to the U.S. unlike any other, Rep. Liz Cheney said, telling her fellow Republicans that if they choose to back Trump's lies about a stolen election, they're also undermining the country. Her party is facing an existential choice, she said.

"Republicans cannot both be loyal to Donald Trump and loyal to the Constitution," Cheney said in a speech at the Ronald Reagan Presidential Library and Museum in Simi Valley, Calif.

Cheney, R-Wyo., is the vice chair of the House Jan. 6 committee. She spoke one day after Cassidy Hutchinson, a former aide to Trump White House Chief of Staff Mark Meadows, shared shocking details about Trump's actions on the day of the insurrection, including demanding that metal detectors be taken away so his armed supporters wouldn't have to worry about surrendering their weapons.

"We are confronting a domestic threat we have never faced before," Cheney said. "And that is a former president who is attempting to unravel the foundations of our constitutional republic. And he is aided by Republican leaders and elected officials who have made themselves willing hostages to this dangerous and irrational man."

"Some in my party are embracing former President Trump. And even after all we have seen, they are enabling his lies," she said. But the threat is too great to condone or ignore, Cheney added.

Hutchinson — whose testimony also detailed Trump's temper tantrums, and an account of the president attempting to take control of his limousine — is just one of the young women who have come forward to testify, Cheney said. They include people who worked on the Trump campaign, in the Trump White House and on Capitol Hill, she added.

Cheney contrasted Hutchinson's patriotism and bravery in speaking out to "her superiors, men many years older. A number of them are hiding behind executive privilege, anonymity, and intimidation."

Cheney also urged girls and young women to aspire to leadership roles, saying they're vitally needed.

"These days, for the most part, men are running the world," she said with a wry smile. "And it is really not going that well."

Acknowledging policy differences she has with Democrats, Cheney criticized President Biden's administration for its handling of the economy and other issues. But, she said, the country now stands at the edge of an abyss, "and we must pull back."

"One of my Democratic colleagues said to me recently that he looked forward to the day when he and I could disagree again," she added. "And believe me, I share that sentiment. Because when we can disagree again about substance and policy, that will mean that our politics have righted themselves" and toxicity, racism and anti-democratic forces have been rejected.

The American people should demand excellence from their elected officials, Cheney said, echoing an idea from earlier in her speech: "We must not elect people who are more loyal to themselves or to power than they are to our Constitution."

The sentiment, which once might have seemed a matter of course in U.S. politics, drew a round of cheers and sustained applause.