WASHINGTON (AP) — One day later, the violent siege of the U.S. Capitol by President Donald Trump's supporters forced painful new questions across government — about his fitness to remain in office for two more weeks, the ability of the police to secure the complex and the future of the Republican Party in a post-Trump era.

In the immediate aftermath, the attack on the world's iconic dome of democracy, shocking imagery flashed around the globe, reinforced lawmakers' resolve to stay up all night to finish counting the Electoral College vote confirming Democrat Joe Biden won the presidential election.

But the rampage that left four dead and a country on edge is forcing a broader reckoning of all that has happened over Trump's tenure in office and what comes next for a tattered and torn nation.

House Speaker Nancy Pelosi said that any remaining day with the president in power could be "a horror show for America."

One Republican lawmaker publicly called for invoking the 25th Amendment to the Constitution, joining Democrats trying to force Trump from office before Biden is inaugurated on Jan. 20. Other lawmakers said there must be a review of the U.S. Capitol Police's failure to stop the the breach by the protesters.

The Republicans who have echoed Trump's false claims of a fraudulent election, including rising stars and some party leaders, face angry, unsettled peers --- but also those cheering them on.

Pelosi said if the president's Cabinet does not swiftly invoke the 25th Amendment, the House may proceed to impeach him. The 25th Amendment allows for the vice president and a majority of the Cabinet to declare the president unfit for office. The vice president then becomes acting president.

The Senate's top Democrat, Chuck Schumer of New York, said Trump must not stay president "one day" longer. He said the attack on the Capitol was "an insurrection against the United States, incited by the president."

With tensions high, the Capitol shuttered and lawmakers not scheduled to return until the inauguration, an uneasy feeling of stalemate settled over a main seat of national power as Trump remained holed up at the White House.

The social media giant Facebook banned the president from its platform and Instagram for the duration of Trump's final days in office, if not indefinitely, citing his intent to stoke unrest. Twitter had silenced him the day before.

Facebook founder Mark Zuckerberg said "the shocking events of the last 24 hours" make it clear Trump "intends to use his remaining time in office to undermine the peaceful and lawful transition of power."

The head of the U.S. Capitol Police Chief Steven Sund faced pressure from Schumer, Pelosi and others in Congress to resign. The sergeants at arms of the House and Senate that oversee the police and security at the complex are also expected to be removed.

Sund defended his department's response to the storming of the Capitol, saying that officers had "acted valiantly when faced with thousands of individuals involved in violent riotous actions."

In his first public comment on the mayhem, Sund said in a statement that rioters "actively attacked" Capitol police and other law enforcement officers with metal pipes, discharged chemical irritants and "took up other weapons against our officers."

It was "unlike any I have ever experienced in my 30 years in law enforcement here in Washington, D.C.," said Sund, a former city police officer.

But Washington Mayor Muriel Bowser quickly called the police response "a failure."

Lawmakers from both parties pledged to investigate law enforcement's actions and questioned whether a lack of preparedness allowed a mob to occupy and vandalize the building.

Black lawmakers, in particular, noted the way the mostly white Trump supporters were treated as they laid siege to the Capitol.

Urged on by Trump during a rally near the White House earlier in the day Wednesday to head to Capitol Hill, protesters swiftly broke through police barriers, smashed windows and paraded through the halls, sending lawmakers into hiding.

The protesters ransacked the place, taking over the House and Senate chambers and waving Trump, American and Confederate flags. Outside, they scaled the walls and balconies in their breach of the building.

Newly elected Rep. Cori Bush, D-Mo., said if "we, as Black people did the same things that happened .... the reaction would have been different, we would have been laid out on the ground, there would have been, there would have been shootings, there would have been people in jail."

One protester, a white woman, was shot to death by Capitol Police, and there were dozens of arrests. Three other people died after "medical emergencies" related to the breach.

Rep. Val Demings, D-Fla., a former police chief, said it was "painfully obvious" that Capitol police "were not prepared" for what took place.

Rep. Tim Ryan, D-Ohio, who is the chairman of a subcommittee that oversees the Capitol police budget, suggested there would be leadership changes on the force.

"I think it's pretty clear that there's going to be a number of people who are going to be without employment very, very soon because this is an embarrassment," he said.

Before dawn Thursday, Congress confirmed Biden as the presidential election winner, lawmakers resolved to return from shelter to show the country, and the world, of the nation's enduring commitment to uphold the will of the voters and the peaceful transfer of power.

Vice President Mike Pence, presiding over the joint session, announced the tally for Biden, 306-232.

Trump, who had repeatedly refused to concede the election, said in a statement immediately after the vote that there will be an "orderly transition" on Inauguration Day.

Several lawmakers suggested that Trump be prosecuted for a crime, impeached for a second time or even removed under the Constitution's 25th Amendment, which seemed unlikely two weeks from when his term expires. The House impeached Trump in 2019 and the Senate acquitted him in 2020.

While Democrats led the charge to invoke the 25th Amendment, similar conversations among Republicans within the administration had made their way to Capitol Hill.

Republican Rep. Adam Kinzinger of Illinois, publicly called on Trump's Cabinet to invoke the 25th Amendment and remove the president from office.

"The president caused this," Kinzinger said in a video posted to Twitter. "The president is unwell."

The 25th Amendment allows for the vice president and a majority of the Cabinet to declare the president unfit for office. The vice president then becomes acting president.

The Republicans who led the effort to challenge the Electoral College tally for Biden exposed the extent of the divisions within the party, and the nation, after four years of Trump's presidency.

Those two GOP senators, Ted Cruz of Texas and Josh Hawley of Missouri, faced angry peers in the Senate.

Cruz in a statement defended his objection to the election results as "the right thing to do" as he tried unsuccessfully to have Congress launch an investigation.

But in the House, Republican leaders Rep. Kevin McCarthy of California and Rep. Steve Scalise of Louisiana, joined in the effort to overturn Biden's win by objecting to the Electoral College results.

Despite Trump's repeated claims of voter fraud, election officials and his own former attorney general have said there were no problems on a scale that would change the outcome. All the states have certified their results as fair and accurate, by Republican and Democratic officials alike.

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Associated Press writers Mary Clare Jalonick, Zeke Miller, Alan Fram, Padmananda Rama and Michael Balsamo in Washington contributed to this report.