US Democrats plan to introduce an article of impeachment against President Donald Trump for his role in Wednesday's invasion of the US Capitol.
House Speaker Nancy Pelosi said she would move forward with impeachment if Mr Trump did not resign immediately.
The charge of "incitement of insurrection" is set to be introduced by House Democrats on Monday.
They accuse Mr Trump of encouraging a riot in Congress in which five people died.
President-elect Joe Biden said impeachment was for Congress to decide, but said he had thought "for a long time President Trump was not fit to hold the job".
The White House dismissed the impeachment as a "politically motivated" move that would "only serve to further divide our great country".
If the process does go ahead, it would be the second time the House of Representatives has pursued impeachment against President Trump.
In December 2019, the House impeached Mr Trump on charges of abuse of power and obstruction of Congress. But the Senate acquitted him on both charges in February 2020.
No US president has ever been impeached twice. However, the prospect of an impeachment conviction is remote because of Mr Trump's Republican support in the Senate.
That means an impeachment in the House would only be a symbolic action to hold Mr Trump accountable for the invasion of Congress.
The unprecedented move comes as Mr Trump's administration plunged deeper into crisis on Friday, as more officials resigned in protest over the riot, and prominent Republicans disavowed the president.
The siege of the Capitol has put senior politicians on edge, prompting the Democratic Speaker Pelosi to talk to the nation's top military officer about ways to prevent Mr Trump from accessing nuclear codes.
In a dramatic day in Washington DC on Friday, other developments included:
Mr Trump has said he would not attend the inauguration of his successor, Mr Biden, on 20 January
The FBI joined an investigation into the death of police officer Brian Sicknick from injuries sustained during the siege of the Capitol.
Dozens of people were arrested and several charged in relation to the assault on the Capitol building
Twitter said it had permanently suspended the account of President Trump, citing "the risk of further incitement of violence"
One of Ms Pelosi's staff members revealed that a laptop was stolen from her office during the mob invasion
Democrats and several prominent Republicans reiterated their calls for Mr Trump's his cabinet to invoke constitutional powers and remove him from office.