Liz Cheney, the No.3 Republican in the House of Representatives, said: “There has never been a greater betrayal by a president of the United States of his office and his oath to the Constitution,” as the Democratic-led chamber moved forward on a path to remove Trump from office.

Trump “summoned this mob, assembled the mob and lit the flame of this attack” on the Capitol last Wednesday, Cheney, the daughter of former Republican vice-president Dick Cheney, said in a statement, adding: “I will vote to impeach the president.”

Two other Republican House members, John Katko and Adam Kinzinger, said they would also vote for the historic second impeachment of the Republican president, who leaves office in just eight days.

Their announcements came as Republican leaders in the US House of Representatives on Tuesday refrained from urging their members to vote against impeaching Trump, saying it was a matter of individual conscience after his supporters ransacked the Capitol.

US Vice-President Mike Pence today ruled out invoking the 25th Amendment to remove Trump from power.

Section 4 of the 25th Amendment is a never-used power that allows a majority of the cabinet to strip the president of power if he or she is deemed unable to discharge the office’s duties.

In a letter to House Speaker Nancy Pelosi, Pence said the mechanism should not be used “as a means of punishment or usurpation” and was reserved for cases of medical or mental incapacitation.

Pelosi had called on Pence to secure the majority of the cabinet and vote to declare Trump unfit to serve.

The New York Times reported the Republican majority leader of the 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 last week’s stunning attack on Congress.

McConnell believed the impeachment effort would make it easier to purge Trump from the party, the Times said.

Making his first public appearance since last Wednesday’s riot, Trump showed no contrition for his remarks to supporters at a rally before they stormed the seat of Congress and also lambasted Democrats for pushing ahead with a drive to impeach him for an unprecedented second time.

“What I said was totally appropriate,” Trump told reporters as he left for the US-Mexico border wall near Alamo, Texas, his first public foray since the assault on the Capitol. “I want no violence.”

In a debate before the House vote on the 25th Amendment resolution, Democrats pushed Republicans to disavow Trump’s false allegation that Democratic President-elect Joe Biden’s victory in the November 3 election was illegitimate – the claim that enraged Trump’s supporters and prompted the violence in Washington that killed five including a police officer.

Republicans refused to concede the point and said their unsuccessful effort last week to challenge the results of the election was justified.

With only eight days left in Trump’s term, chances the Democratic push will result in his removal before Biden takes office on January 20 appear remote. But Democrats say Trump’s actions demand a response.

Democrats could also use an impeachment trial to push through a vote blocking Trump from running for office again.

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 50-50 chamber would have to vote for conviction.

But only a simple majority is needed to disqualify Trump from future office.

Democrats said that if Trump had not stepped down or Pence had not taken action they planned to bring impeachment to the House floor.

McConnell has said no trial could begin until the chamber returns from recess on January 19.

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.

-with AAP