WASHINGTON (AP) — President Donald Trump's impeachment trial could begin on Inauguration Day, just as Democrat Joe Biden takes the oath of office in an ever-more-extraordinary end to the defeated president's tenure in the White House.

The timing is not set and depends heavily on when House Speaker Nancy Pelosi decides to transmit the article of impeachment to the Senate. Democrats hoping to avoid interrupting Biden's inauguration have suggested holding back until the new president has a chance to get his administration going.

What is clear is that the trial will be unlike any other in the nation's history, the first for a president no longer in office. And, politically, it will force a reckoning among some Republicans who have stood by Trump throughout his presidency and largely allowed him to spread false attacks against the integrity of the 2020 election.

“The only path to any reunification of this broken and divided country is by shining a light on the truth," said Rep. Madeleine Dean, D-Pa., who will serve as an impeachment manager.

"That’s what the impeachment vote was. That’s what the trial in the Senate will be about.”

Trump was impeached Wednesday by the House over the deadly Capitol siege, the only president in U.S. history twice impeached, after a pro-Trump mob stormed the building. The attack has left the nation’s capital, and other major cites, under high security amid threats of more violence around the inauguration.

Senate Republican leader Mitch McConnell is open to considering impeachment, having told associates he is done with Trump, but he has not signaled how he would vote.

The Republican leader holds great sway in his party even though convening the trial will be among his last acts as majority leader. Two new senators from Georgia, both Democrats, are to be sworn into office leaving the chamber divided 50-50. That tips the majority to the Democrats once Kamala Harris takes office, as the vice president is a tie-breaker.

No president has ever been convicted in the Senate, and it would take a two-thirds vote against Trump, an extremely tall hurdle. But it's not out of the realm of possibility, especially as corporations and wealthy political donors distance themselves from Trump and the Republicans who stood by his attempt to overturn the election.

At least four Republican senators have publicly expressed grave concerns about Trump's actions, and others say so privately.

Under Senate procedure, the trial is to start soon after the House delivers the article of impeachment. That could mean starting at 1 p.m. on Inauguration Day. The ceremony at the Capitol starts at noon.

Pelosi has not said when she will take the next step to transmit the impeachment article, a sole charge of incitement of insurrection. After Trump's first impeachment, in 2019, she withheld the articles for some time to set the stage for the Senate action.

Biden has said the Senate should be able to split its time and do both — hold the trial and start working on his priorities, including swift confirmation of his Cabinet nominees.

On Inauguration Day, the Senate typically confirms some of the new president's Cabinet, particularly national security officials. Biden's choice of Avril Haines as director of national intelligence will have a hearing Friday by the Senate Intelligence Committee.

“We are working with Republicans to try to find a path forward,” said Senate Democratic leader Chuck Schumer's office.

With the Capitol secured by armed National Guard troops inside and out, the House voted 232-197 on Wednesday to impeach Trump. The proceedings moved at lightning speed, with lawmakers voting just one week after violent pro-Trump loyalists stormed the Capitol, egged on by the president’s calls for them to “fight like hell” against the election results.

Ten Republicans fled Trump, joining Democrats who said he needed to be held accountable and warned ominously of a “clear and present danger” if Congress should leave him unchecked before Biden’s inauguration Jan. 20. It was the most bipartisan presidential impeachment in modern times.

The Capitol insurrection stunned and angered lawmakers, who were sent scrambling for safety as the mob descended, and it revealed the fragility of the nation’s history of peaceful transfers of power.

Holed up at the White House, watching the proceedings on TV, Trump later released a video statement in which he made no mention at all of the impeachment but appealed to his supporters to refrain from any further violence or disruption of Biden's inauguration.

“Like all of you, I was shocked and deeply saddened by the calamity at the Capitol last week," he said, his first condemnation of the attack. He said, "Mob violence goes against everything I believe in and everything our movement stands for. ... No true supporter of mine could ever disrespect law enforcement.”

Trump was first impeached by the House in 2019 over his dealings with Ukraine, but the Senate voted in 2020 to acquit. This time he faces impeachment as a weakened leader, having lost his own reelection as well as the Senate Republican majority.

In making a case for the “high crimes and misdemeanors” demanded in the Constitution, the four-page impeachment resolution relies on Trump’s own incendiary rhetoric and the falsehoods he spread about Biden’s election victory, including at a rally near the White House on the day of the Jan. 6 attack on the Capitol.

The impeachment resolution is also intended to prevent Trump from ever running again.

A Capitol Police officer died from injuries suffered in the riot, and police shot and killed a woman during the siege. Three other people died in what authorities said were medical emergencies. The riot delayed the tally of Electoral College votes that was the last step in finalizing Biden’s victory.

Ten Republican lawmakers, including third-ranking House GOP leader Liz Cheney of Wyoming, voted to impeach Trump, cleaving the Republican leadership, and the party itself. She said that "there has never been a greater betrayal by a President” of his office.

The president’s sturdy popularity with the GOP lawmakers’ constituents still had some sway, and most House Republicans voted not to impeach.

Security is exceptionally tight at the Capitol, with tall fences around the complex. Metal-detector screenings were required Wednesday for lawmakers entering the House chamber, where a week earlier some of them huddled inside as police, guns drawn, barricaded the door from rioters.

The impeachment bill draws from Trump’s own false statements about his election defeat to Biden. Judges across the country, including some nominated by Trump, have repeatedly dismissed cases challenging the election results, and former Attorney General William Barr, a Trump ally, has said there was no sign of widespread fraud.

While some have questioned impeaching the president so close to the end of his term, there is precedent. In 1876, during the Ulysses Grant administration, War Secretary William Belknap was impeached by the House the day he resigned, and the Senate convened a trial months later. He was acquitted.

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Associated Press writers Kevin Freking, Andrew Taylor, Alan Fram, Zeke Miller and Jonathan Lemire contributed to this report.