The US Senate has resumed debating the Republican challenge against Democrat Joe Biden's presidential election victory, more than six hours after pro-Trump mobs attacked the Capitol and forced lawmakers to flee.
Scores of Republican representatives and 13 GOP senators had planned to object on Wednesday to the electoral votes of perhaps six states that backed Mr Biden.
President Donald Trump has falsely insisted that the election was marred by fraud and that he actually won.
He reiterated those claims in remarks to thousands of protesters outside the White House early on Wednesday and goaded them to march to the Capitol, which many of them did.
The mayhem had forced the House and Senate to abruptly end the day's debates and flee to safety under the protection of police.
Wednesday's ordinarily mundane procedure of Congress certifying a new president was always going to be extraordinary, with Republican supporters of Mr Trump vowing to protest over the results of an election that they have baselessly insisted was reversed by fraud.
But even the unusual deliberations, which included the Republican vice president and Senate majority leader defying Mr Trump's demands, were quickly overtaken.
In a raucous, out-of-control scene, protesters fought past police and breached the building, shouting and waving Trump and American flags as they marched through the halls.
Police said four people died in the protests. Washington DC police chief Robert Contee said the dead included a woman who was shot by US Capitol Police, as well as three others who died in "medical emergencies".
Police said both law enforcement and protesters deployed chemical irritants during the hours-long occupation of the Capitol building before it was cleared by law enforcement.
The woman was shot as the mob tried to break through a barricaded door in the Capitol where police were armed on the other side. She was hospitalised with a gunshot wound and later died.
DC police officials also said two pipe bombs were recovered, one outside the Democratic National Committee and one outside the Republican National Committee.
The protesters abruptly interrupted the congressional proceedings in an eerie scene that featured official warnings directing people to duck under their seats for cover and put on gas masks after tear gas was used in the Capitol Rotunda.
With the crowds showing no signs of abating, President Trump tweeted: "Please support our Capitol Police and Law Enforcement. They are truly on the side of our Country. Stay peaceful!"
Earlier, at his rally, he had urged supporters to march to the Capitol.
It prompted bipartisan outrage as many lawmakers blamed Mr Trump for fostering the violence.
As the Senate reconvened, Senate Democratic leader Chuck Schumer said President Donald Trump "bears a great deal of the blame" for the actions of the mob, adding the events "did not happen spontaneously".
Mr Schumer also said January 6, 2021, will "live forever in infamy" and will be a stain on the democracy.
He said: "The president, who promoted conspiracy theories that motivated these thugs, the president, who exhorted them to come to our nation's capital, egged them on."
House speaker Nancy Pelosi said Congress' certification of President-elect Joe Biden's election win will show the world it will not back down.
Multiple Republican senators have reversed course and now say they will not object to congressional certification of President-elect Joe Biden's victory.
Senators Steve Daines of Montana, Mike Braun of Indiana and Kelly Loeffler of Georgia all said in light of the violence they would stand down from planned objections to Mr Biden's win.
Ms Loeffler said that the "violence, the lawlessness, and siege of the halls of Congress" were a "direct attack" on the "sanctity of the American democratic process".
All three had previously signed on to Mr Trump's false claims of widespread voter fraud to explain his defeat.
Both the Senate and the House voted overwhelmingly to reject an objection to Mr Biden's win in Arizona.
Other objections to results from Georgia, Michigan and Nevada fizzled without adequate support from senators.
An objection to Pennsylvania backed by Republican senators Josh Hawley and Scott Perry forced deliberations, though senators quickly derailed the attempt to overturn the state's support for the Democrat.