US House Speaker Nancy Pelosi speaks during a press conference on Capitol Hill in Washington, D.C., the United States, on Sept. 17, 2020. (Photo by Ting Shen/Xinhua)

Congressional Democrats on Monday began their drive to force President Donald Trump from office, kicking off a week of action that could end with a vote that would make him the only president in US history to be impeached twice.

Thousands of Trump supporters stormed the Capitol last week, scattering lawmakers who were certifying Democratic President-elect Joe Biden's election victory, in a harrowing assault on the center of US democracy that left five dead.

The violence came after Trump urged supporters to march on the Capitol at a rally where he repeated false claims that his resounding election defeat was illegitimate. 

House of Representatives Speaker Nancy Pelosi, many of her fellow Democrats and a handful of Republicans say Trump should not be trusted to serve out his term, which ends on January 20.

"In protecting our Constitution and our Democracy, we will act with urgency, because this President represents an imminent threat to both," Pelosi wrote to fellow House Democrats on Sunday.

Dozens of people who attacked police officers, stole computers and smashed windows at the Capitol have been arrested for their role in the violence, and officials have opened 25 domestic terrorism investigations.

Trump acknowledged that a new administration would take office on January 20 in a video statement after the attack, but has not appeared in public. Twitter and Facebook have suspended his accounts, citing the risk of him inciting violence.

As the House was expected to convene at 11 am (1600 GMT) on Monday, lawmakers were to bring up a resolution asking Vice President Mike Pence to invoke the never-used 25th Amendment of the US Constitution, which allows the vice president and the Cabinet to remove a president deemed unfit to do the job. A recorded vote is expected on Tuesday.

Pence was in the Capitol along with his family when Trump's supporters attacked, and he and Trump are currently not on speaking terms. 

But Republicans have shown little interest in invoking the 25th Amendment. 

A source said last week he was opposed to the idea.

Even if the House impeaches Trump for a second time, the Senate would not take up the charges until January 19 at the earliest, Trump's last full day in office.