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)

Speaker Nancy Pelosi of the US House of Representatives said on Sunday that Democrats are ready to start proceedings to impeach outgoing President Donald Trump for a second time in just over a year.

In a letter to her colleagues, Pelosi said Democrats will introduce a resolution on Monday urging Vice President Mike Pence to "convene and mobilize the Cabinet to active the 25th Amendment to declare the President incapable of executing the duties of his office," after which Pence would immediately exercise powers as acting US president.

"We are calling on the Vice President to respond within 24 hours," the top congressional Democrat wrote. "Next, we will proceed with bringing impeachment legislation to the Floor."

The announcement came as Trump is facing fierce bipartisan criticism for a role in massive demonstrations on Capitol Hill last week that led to at least five deaths and dozens of injuries following a chaotic and violent breach of the historic building when Congress was certifying President-elect Joe Biden's victory in the 2020 White House race.

Trump addressed a rally outside the White House shortly before the deadly violence unfolded, urging his supporters to march toward the landmark to encourage Republican lawmakers to contest the Electoral College results, as he had refused to acknowledge their legitimacy with unsubstantiated claims of voter fraud.

Supporters of U.S. President Donald Trump gather near the U.S. Capitol building in Washington, D.C., the United States, Jan. 6, 2021. (Xinhua/Liu Jie)

 
House Democrats have announced they plan to bring forward at least one article of impeachment against Trump this week, accusing him of "incitement of insurrection" at the Capitol.

Meanwhile, several Republicans have joined Democrats in calling upon the president to resign over the Capitol violence.

The US Constitution provides that the House "shall have the sole Power of Impeachment" and that "the Senate shall have the sole Power to try all Impeachments." Through the impeachment process, the US Congress charges and then tries an official of the federal government for "Treason, Bribery, or other high Crimes and Misdemeanors."

Conviction can only happen in the Senate and requires at least two-thirds of its members, or 67 senators, to vote in favor of at least one article of impeachment after a trial. The chamber could try the impeachment of an official after he or she leaves office, legal experts said.

The House, led by Democrats, impeached Trump in December 2019 after an inquiry triggered by a whistleblower complaint that raised concerns about the White House's interactions with Ukraine. The Republican-led Senate later acquitted the president, allowing him to continue holding office.

No US president has ever been removed from office via impeachment by Congress, nor has the House impeached any president more than once.

On Jan. 7, the US Congress affirmed the 2020 Electoral College votes, in which Biden won 306 versus 232 for Trump. It takes at least 270 electoral votes to win the White House. Biden also won the popular votes by 7 million and more than 4 percentage points.

After the congressional certification of Biden's victory, Trump acknowledged defeat and promised to ensure "a smooth, orderly and seamless transition of power."