With at least four Republicans joining a push to impeach Donald Trump over the storming of the US Capitol, Democrats in the House of Representatives are poised for a vote to try to remove the president from office.
With eight days left in Trump's term, the House will vote on Wednesday on an article of impeachment accusing the Republican of inciting insurrection in a speech to followers last week before a mob stormed the Capitol, leaving five dead.
That would trigger a trial in the still Republican-controlled Senate, although it was unclear whether enough time or political appetite remained to expel Trump.
Democrats moved forward on an impeachment vote after a effort to persuade Vice President Mike Pence to invoke the 25th Amendment of the US Constitution to remove Trump was rejected by Pence on Tuesday evening.
"I do not believe that such a course of action is in the best interest of our Nation or consistent with our Constitution," Pence said in a letter to House Speaker Nancy Pelosi.
Despite the letter, the House passed a resolution formally calling on Pence to act. The final vote was 223-205 in favour.
While that was occurring, Trump's iron grip on his party was showing further signs of slipping as at least four Republicans, including a member of the House leadership, said they would vote for his second impeachment - a prospect no president before Trump has faced.
Representative Liz Cheney, the No. 3 House Republican, said: "There has never been a greater betrayal by a President of the United States of his office and his oath to the Constitution."
Trump "summoned this mob, assembled the mob, and lit the flame of this attack" on the Capitol on January 6, Cheney, the daughter of former Republican Vice President Dick Cheney, said in a statement, adding: "I will vote to impeach the president."
Three other Republican House members, John Katko, Adam Kinzinger and Fred Upton, said they would also vote for impeachment.
"What I said was totally appropriate," Trump told reporters on Tuesday in his first public foray since the assault on the Capitol.
At a meeting to set the rules for Wednesday's impeachment vote, Democratic Representative David Cicilline told the House Rules Committee that the impeachment drive had the support of 217 lawmakers - enough to impeach Trump.
House Republicans who opposed the impeachment drive argued Democrats were going too far, as Trump was on the verge of leaving office.
The New York Times reported that the Republican majority leader of the US Senate, Mitch McConnell, was said to be pleased about the Democratic impeachment push, suggesting Trump's party was looking to move on from him after the attack on Congress.
McConnell believes the impeachment effort will make it easier to purge Trump from the party, the Times said.
If Trump is impeached by the House, he would have a trial in the Senate to determine his guilt. A two-thirds majority of the Senate is needed to convict him, meaning at least 17 Republicans in the 100-member chamber would have to vote for conviction.
Pelosi on Tuesday named nine impeachment "managers," who would present the House's case for impeachment during a Senate trial, but it remained unclear how swiftly such a trial would take place if the House votes to impeach.
McConnell has said no trial could begin until the chamber returns from its recess on January 19, the day before Biden is sworn in as president.
But Democratic Minority Leader Chuck Schumer, who is set to become the majority leader after two Democrats from Georgia are seated and Vice President-elect Kamala Harris is sworn in, told reporters the Senate could be recalled to handle the matter.
Democrats could also use an impeachment trial to push through a vote blocking Trump from running for office again.
Rather than a two-thirds vote, a simple Senate majority is needed to disqualify Trump from future office.
Trump has said he plans to run again in 2024.