Violent protesters loyal to President Donald Trump stormed the U.S. Capitol on Wednesday and forced lawmakers into hiding, in a stunning attempt to overturn America’s presidential election, undercut the nation’s democracy and keep Democrat Joe Biden from replacing Trump in the White House.

The nation’s elected representatives scrambled to crouch under desks and don gas masks, while police futilely tried to barricade the building, one of the most jarring scenes ever to unfold in a seat of American political power. A woman was shot and killed inside the Capitol, and Washington’s mayor instituted an evening curfew in an attempt to contain the violence.

The rioters were egged on by Trump, who has spent weeks falsely attacking the integrity of the election and had urged his supporters to descend on Washington Wednesday to protest Congress’ formal approval of Biden’s victory. Some Republican lawmakers were in the midst of raising objections to the results on his behalf when the proceedings were abruptly halted by the mob.

Together, the protests and the GOP election objections amounted to an almost unthinkable challenge to American democracy and exposed the depths of the divisions that have coursed through the country during Trump’s four years in office. Though the efforts to block Biden from being sworn in on Jan. 20 were sure to fail, the support Trump has received for his efforts to overturn the election results have badly strained the nation’s democratic guardrails.

House Speaker Nancy Pelosi said lawmakers were resuming the counting of electoral votes Wednesday evening after the Capitol was cleared of the pro-Trump occupiers.

The president gave his supporters an added boost Wednesday morning during an appearance at a rally outside the White House, where he urged them to march to the Capitol. He spent much of the afternoon in his private dining room off the Oval Office watching scenes of the violence on television. At the urging of his staff, he reluctantly issued a pair of tweets and a taped video telling his supporters it was time to “go home in peace” — yet he still said he backed their cause.

Hours later, Twitter for the first time time locked Trump’s account, demanded that he remove tweets excusing violence and threatened “permanent suspension.”

A somber President-elect Biden, two weeks away from being inaugurated, said American democracy was “under unprecedented assault,” a sentiment echoed by many in Congress, including some Republicans. Former President George W. Bush said he watched the events in “disbelief and dismay.”

“What happened here today was an insurrection, incited by the President of the United States,” said Republican Sen. Mitt Romney of Utah.

There were harsh words from major business organizations and the Republican National Committee, too, suggesting uneasy relations with Trump were skidding into divorce as he leaves Washington.

“Our soldiers have died carrying the American flag into battle for our freedom,” tweeted RNC communications director Michael Ahrens. “To see that flag used in the name of unfounded conspiracy theories is a disgrace to the nation, and every decent American should be disgusted by it.”

Trump, unrepentant, had tweeted, “These are the things and events that happen when a sacred landslide election victory is so unceremoniously & viciously stripped away from great patriots who have been badly & unfairly treated for so long.”

“Remember this day forever!”

The domed Capitol building has for centuries been the scene of protests and occasional violence, including a 1954 shooting involving Puerto Rican nationalists. But Wednesday’s events were particularly astounding both because they unfolded at least initially with the implicit blessing of the president and because of the underlying goal of overturning the results of a free and fair presidential election.

Tensions were already running high when lawmakers gathered early Wednesday afternoon for the constitutionally mandated counting of the Electoral College results, in which Biden defeated Trump, 306-232. Despite pleas from Republican Senate Majority Leader Mitch McConnell, more than 150 GOP lawmakers planned to support objections to some of the results, though lacking evidence of fraud or wrongdoing in the election.

Trump spent the lead-up to the proceedings publicly hectoring Vice President Mike Pence, who had a largely ceremonial role in the proceedings, to aid the effort. He tweeted on Wednesday: “Do it Mike, this is a time for extreme courage!”

But Pence, in a statement shortly before presiding, defied Trump, saying he could not claim “unilateral authority” to reject the electoral votes that make Biden president.

Shortly after the first GOP objections, protesters fought past police and breached the building, shouting and waving Trump and American flags as they marched through the halls. Lawmakers were told to duck under their seats for cover and put on gas masks after tear gas was used in the Capitol Rotunda. Some House lawmakers tweeted they were sheltering in place in their offices.

Rep. Scott Peters, D-Calif., told reporters he was in the House chamber when rioters began storming it. Security officers “made us all get down, you could see that they were fending off some sort of assault, it looked like. They had a piece of furniture up against the door, the door, the entry to the floor from the Rotunda, and they had guns pulled,” Peters said.

“And they just told us to take our pins off,” he added, referring to lapel pins members wear so Capitol Police can quickly identify them. Then the lawmakers were evacuated.

Staff members grabbed the boxes of Electoral College votes as the evacuation took place. Otherwise, said Sen. Jeff Merkley, D-Ore., the ballots likely would have been destroyed by the protesters.

Trump supporters posting on internet forums popular with far-right fringe elements celebrated the chaos. Messages posted on one turned from profane frustration over the content of Trump’s speech to glee when supporters stormed the building. At least one leading figure was livestreaming video from inside the Capitol during the siege.

The mob’s storming of Congress prompted bipartisan outrage, as lawmakers accused Trump of fomenting the violence with his relentless falsehoods about election fraud. Several suggested that he be prosecuted for a crime, which seems unlikely two weeks from when his term expires.

“I think Donald Trump probably should be brought up on treason for something like this,” Rep. Jimmy Gomez, D-Calif., told reporters. “This is how a coup is started. And this is how democracy dies.”

Sen. Ben Sasse, R-Neb., who’s at times clashed with Trump, issued a written statement saying, “Lies have consequences. This violence was the inevitable and ugly outcome of the President’s addiction to constantly stoking division.”

Pro-Trump demonstrators assembled elsewhere in the country, forcing evacuations in at least two states. Cheers rang out in St. Paul, Minnesota, from demonstrators in reaction to the news that supporters of Trump had stormed the Capitol. New Mexico state police evacuated staff from a statehouse building as a precaution after hundreds of flag-waving supporters arrived in a vehicle caravan and on horseback.

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.

The Pentagon said about 1,100 District of Columbia National Guard members were being mobilized to help support law enforcement at the Capitol. More than a dozen people were arrested.

As darkness began to set in, law enforcement officials worked their way toward the protesters, using percussion grenades to try to clear the area around the Capitol. Big clouds of tear gas were visible. Police in full riot gear moved down the steps, clashing with demonstrators.

The Associated Press contributed to this report.