A protester carries a sign calling for Congress to impeach US President Donald Trump, near Washington, DC on Sunday. Trump faced fresh calls Sunday from some members of his own party to resign over the violent incursion into the US Capitol, as the threat builds for a historic second impeachment effort in his final 10 days in the White House. Photo: VCG

Democrats were giving President Donald Trump one last chance on Tuesday to leave office days before his term expires or face an unprecedented second impeachment over his supporters' deadly January 6 assault on the US Capitol.

The Democratic-led House of Representatives plans to vote as soon as Wednesday on formal charges of misconduct, known as articles of impeachment, unless Trump resigns or Vice President Mike Pence moves to oust him under a provision in the US Constitution.

The House was due to vote on Tuesday on a resolution calling on Pence, a Republican, to invoke within a day the 25th Amendment, a never-before used law that allows a majority of the Cabinet to strip the president of power if he or she is unable to discharge the office's duties. 

Pence advisers say he is opposed to the idea.

The violence at the Capitol caused a serious rift between Trump and Pence, and the two men did not speak for days, although they did meet at the White House on Monday. 

A senior administration ­official said they discussed the riot.

If Trump has not stepped down and Pence has not taken action by Wednesday, Democratic leaders said they will bring his impeachment to the House floor, one week after the riot that forced lawmakers into hiding for hours and left behind five dead, including a police officer.

Meanwhile, US Representative Tom Reed, a moderate Republican, wrote in a New York Times op-ed that he and House colleagues would introduce a censure resolution against Trump on Tuesday as an alternative to a "rushed, divisive" impeachment.

But House Speaker Nancy Pelosi, the top congressional Democrat, told Democratic members on a conference call on Monday that a censure "would be an abdication of our responsibility," according to a source familiar with the call.

Democratic lawmakers introduced one article of impeachment on Monday, accusing Trump of inciting a violent insurrection with a fiery speech exhorting thousands of followers to march to the famous domed building where Congress was working to certify President-elect Joe Biden's November 3 election victory.

With only eight days left in Trump's term, chances that the Democratic drive will result in his removal appear remote.

Impeachment triggers a trial in the Republican-controlled Senate, which is in recess and not scheduled to return to Washington until January 19, the day before Biden is to be sworn in.

A Senate conviction requires a two-thirds vote, which means at least 17 Republicans would have to break with a president who has maintained an iron grip over his party for four years.