Pelosi made the announcement in a letter to colleagues, saying the House will first vote to push Vice President Mike Pence to invoke the powers of the 25th Amendment to remove Trump from office. After 24 hours, she said, the House would proceed with legislation on impeachment. Trump could become the only president to be impeached twice.

"In protecting our Constitution and our Democracy, we will act with urgency, because this President represents an imminent threat to both," she said, and added: "The horror of the ongoing assault on our democracy perpetrated by this President is intensified and so is the immediate need for action."

On Monday, Pelosi's leadership team will seek a vote on a resolution calling on Pence and Cabinet officials to invoke the 25th Amendment.

If it were to pass, Pence and the Cabinet would have 24 hours to act before the House would move toward impeachment.

David Cicilline, a leader of the House effort to draft impeachment articles accusing Trump of inciting insurrection, said on Sunday his group had 200-plus co-sponsors.

Two Republican senators have said they want Trump to resign immediately in the wake of the violence at the Capitol. The president whipped up the mob that stormed the Capitol, sent lawmakers into hiding and left five dead.

Senator Pat Toomey of and Senator Lisa Murkowski of Alaska are both calling for Trump to "resign and go away as soon as possible."

"I think the president has disqualified himself from ever, certainly, serving in office again," Toomey said. "I don't think he is electable in any way."

House Democrats were expected to introduce articles of impeachment on Monday. The strategy would be to condemn the president's actions swiftly but delay an impeachment trial in the Senate for 100 days. That would allow President-elect Joe Biden to focus on other priorities as soon as he is inaugurated on January 20.

During an interview on "60 Minutes" aired Sunday, Pelosi invoked the Watergate era when Republicans in the Senate told President Richard Nixon, "It's over."

"That's what has to happen now," she said.

While many have criticised Trump, Republicans have said that impeachment would be divisive in a time of unity.

Senator Marco Rubio said that instead of coming together, Democrats want to "talk about ridiculous things like 'Let's impeach a president'" with just days left in office.

Still, some Republicans might be supportive.

Nebraska Sen. Ben Sasse said he would take a look at any articles that the House sent over. Illinois Rep. Adam Kinzinger, a frequent Trump critic, said he would "vote the right way" if the matter were put in front of him.

The articles, if passed by the House, could then be transmitted to the Senate for a trial, with senators acting as jurors to acquit or convict Trump. If convicted, Trump would be removed from office and succeeded by the vice president. It would be the first time a US president had been impeached twice.

Australian Associated Press