Democrats will proceed with plans to impeach President Donald Trump in the aftermath of riots at the nation's capital unless action is taken by vice president Mike Pence and the Republican Party to force him out with just more than a week before the end of his term.

House Speaker Nancy Pelosi made her announcement in a letter to members of Congress early Monday - calling for an end to "the ongoing assault of our democracy perpetrated by this president."

Last week 147 Republicans objected to election winner Joe Biden being declared the next U.S. president - in doing so they tacitly endorsed Trump's electoral fraud conspiracy theory that prompted the Jan. 6 riot in Congress resulting in six deaths and more than 50 arrests.

The Democrat-controlled House of Representatives will vote to force Pence to invoke the constitutional authority, the 25th Amendment, to declare Trump as unfit for office and strip him of power.

The full assembly is unlikely to be convened Monday in the U.S. - meaning any objections raised by Republican Representatives will scupper the resolution and force Pelosi to bring it before the House again Tuesday when all members will be present.

If the resolution passes, the speaker will give Pence 24 hours to invoke the 25th Amendment before restarting an impeachment process in the Senate.

Ratified in 1967 following the death of President Kennedy, the 25th Amendment outlines how a president or vice president can be replaced if they resign, die or are unable to fulfill the demands of their office.

Democrats are hoping to use section four of the amendment, giving the vice president and cabinet the authority to remove the president from power on the back of Trump's willingness to start an insurrection and undermine the peaceful transfer of power.

Longtime supporters like Republican Senator Lisa Murkowski of Alaska are abandoning Trump in the wake of the uprising by his followers. The president should "resign and go away as soon as possible," Murkowski said late Sunday.

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

While many Republicans have spoken against Trump in recent days, their support for a second impeachment attempt is not guaranteed.

"I don't think anybody can look and say an impeachment of this president is the thing that's going to help unite and bring our country together," Republican House Representative Steve Scalise said late Sunday.

But according to political scientist Seth Masket, uniting the country is not the biggest concern for lawmakers at the moment. "Impeachment is to remove a danger from the government, whether that brings unity or division," he wrote on Twitter.

If Pelosi succeeds, Trump will become the only president to be put on trial for impeachment twice.