WASHINGTON — The chairman of the House committee investigating the Jan. 6, 2021, insurrection at the U.S. Capitol and Donald Trump’s effort to overturn the 2020 election opened Thursday’s prime-time hearing declaring the attack an “attempted coup” that put “two and half centuries of constitutional democracy at risk.”

Rep. Bennie Thompson, D-Miss., said “the world is watching” the U.S. response to the panel’s yearlong investigation into the riot and the defeated president’s extraordinary effort to stop Congress from certifying Joe Biden’s election victory. He called it a “brazen attempt” to overturn the election.

“Democracy remains in danger,” Thompson said. “We must confront the truth with candor, resolve and determination.”

The committee was presenting never-before-seen video and a mass of other evidence, aiming to show the “harrowing story” of the deadly violence that day and also a chilling backstory as Trump, the defeated president, tried to overturn Biden’s election victory.

In one clip, the panel played a quip from former Attorney General Bill Barr who testified that he told Trump the claims of a rigged election were “bull----.”

Thursday night’s hearing was providing eyewitness testimony from the first police officer pummeled in the mob riot and from a documentary filmmaker who tracked the extremist Proud Boys as they prepared to fight for Trump immediately after the election and then led the storming of the Capitol.

The hearing also featured accounts from Trump aides and family members, interviewed behind closed doors.

There was an audible gasp in the hearing room, when vice chair Liz Cheney, R-Wyo., read an account that said when Trump was told the Capitol mob was chanting for Vice President Mike Pence to be hanged, Trump responded that maybe they were right, that he “deserves it.”

Trump was angry that Pence did not refuse to accept the certification of Biden’s victory.

The panel’s findings aim to show that America’s tradition of a peaceful transfer of presidential power came close to slipping away. They reconstruct how Trump refused to concede the election, spread false claims of voter fraud and orchestrated an unprecedented public and private campaign to overturn Biden’s victory.

Trump, unapologetic, dismissed the investigation anew — and even declared on social media that Jan. 6 “represented the greatest movement in the history of our country.”

The result of the coming weeks of public hearings may not change hearts or minds in politically polarized America. But the committee’s investigation with 1,000 interviews is intended to stand as a public record for history. A final report aims to provide an accounting of the most violent attack on the Capitol since the British set fire to it in 1814, and to ensure such an attack never happens again.

The riot left more than 100 police officers injured, many beaten and bloodied, as the crowd of pro-Trump rioters, some armed with pipes, bats and bear spray, charged into the Capitol. At least nine people who were there died during and after the rioting, including a woman who was shot and killed by police.

Against this backdrop, the committee is speaking to a divided America, ahead of the fall midterm elections when voters decide which party controls Congress. Most TV networks were carrying the hearing live, but Fox News Channel was not.

Among those in the audience were several current and former police officers who fought the mob in a desperate battle to protect the Capitol and lawmakers who were trapped together in the House gallery during the siege have stayed close.

“We want to remind people, we were there, we saw what happened,” said Rep. Dean Phillips, D-Minn. “We know how close we came to the first non-peaceful transition of power in this country.”

Thompson opened the hearing with a sweep of American history, saying he heard in those denying the stark reality of Jan. 6 his own experience growing up in a time and place “where people justified the action of slavery, the Ku Klux Klan and lynching.”

He and Cheney, the daughter of former Vice President Dick Cheney, outlined what the committee has learned about the events leading up to the day when Trump sent his supporters to Congress to “fight like hell” for his presidency as lawmakers undertook the typically routine job of certifying the previous November’s results.

One witness scheduled Thursday was documentary maker Nick Quested, who filmed the Proud Boys storming the Capitol — along with a meeting between the group’s then-chairman Henry “Enrique” Tarrio and another extremist group, the Oath Keepers, the night before in a nearby parking garage.

Court documents show that members of the Proud Boys and Oath Keepers were discussing as early as November a need to fight to keep Trump in office. Leaders of both groups and some members have since been indicted on rare sedition charges.