WASHINGTON — House Democrats prosecuting Donald Trump's impeachment said Thursday the Capitol invaders believed they were are acting on "the president's orders" to storm the building and stop the joint session of Congress that was certifying Democrat Joe Biden's election.

The prosecutors are wrapping up their opening presentation, describing in stark, personal terms the horror they faced that day and drilling down on the public and explicit instructions Trump gave his supporters — both in the weeks before the Jan. 6 attack and at his midday rally that unleashed the mob on the Capitol. They presented videos of rioters, some posted to social medial by the rioters themselves, talking about how they were doing it all for Trump. 

"They truly believed that the whole intrusion was at the president's orders," said Rep. Diana DeGette of Colorado. "The president told them to be there."

Trump's lawyers will launch their defense on Friday.

At the White House, President Joe Biden said he believed "some minds may be changed" after senators saw chilling security video Wednesday of the deadly insurrection at the Capitol, including of rioters searching menacingly for House Speaker Nancy Pelosi and Vice President Mike Pence.

Biden said he didn't watch any of the previous day's proceedings live but later saw news coverage.

The never-before-seen audio and video released Wednesday is now a key exhibit in Trump's impeachment trial as lawmakers prosecuting the case argue Trump should be convicted of inciting the siege.

Democrats are using their remaining hours of arguments to lay out the physical and mental harm caused by the attack, discuss Trump's lack of action as it unfolded and do a final presentation on the legal issues involved.

Videos of the siege have been circulating since the day of the riot, but the graphic compilation shown to senators Wednesday amounted to a more complete narrative, a moment-by-moment retelling of one of the nation's most alarming days. It offered fresh details into the attackers, scenes of police heroism and staff whispers of despair. And it showed how close the country came to chaos over the certification of Trump's defeat to Biden.

The footage showed the mob smashing into the building, rioters engaging in hand-to-hand combat with police and audio of Capitol police officers pleading for back-up. It underscored how dangerously close the rioters came to the nation's leaders, shifting the focus of the trial from an academic debate about the Constitution to a raw retelling of the assault.

Rioters were seen roaming the halls chanting "Hang Mike Pence," some equipped with combat gear. Outside, the mob had set up a makeshift gallows. And in one wrenching moment, police were shown shooting and killing a San Diego woman, Ashli Babbitt, as the mob tried to break through doors near the House Chamber.

Pence, who had been presiding over a session to certify Biden's election victory over Trump — thus earning Trump's censure — was shown being rushed to safety, where he sheltered in an office with his family just 100 feet from the rioters. Pelosi was seen being evacuated from the complex as her staff hid behind doors in her suite of offices.

Though most of the Senate jurors seem to have made up their minds, making Trump's acquittal likely, they sat riveted as the jarring video played in the chamber. Republican Sen. James Lankford of Oklahoma bent his head at one point, another GOP colleague putting his hand on his arm in comfort.

"President Trump put a target on their backs and his mob broke into the Capitol to hunt them down," said House prosecutor Stacey Plaskett, the Democratic delegate representing the Virgin Islands.

Sen. Mitt Romney, R-Utah, saw himself in the footage, dashing down a hallway to avoid the mob. Romney said he hadn't realized that officer Eugene Goodman, who has been praised as a hero for luring rioters away from the Senate doors, had been the one to direct him to safety.

"That was overwhelmingly distressing and emotional," he said. 

Earlier in the day, prosecutors laid out their case by methodically linking Trump's verbal attacks on the election to the violence that resulted. Trump did nothing to stem the violence and watched with "glee," the Democrats said, as the mob ransacked the building. Five people died. 

The goal of the presentation was to cast Trump not as an innocent bystander but rather as the "inciter in chief" who spent months spreading falsehoods about the election. Using evocative language meant to match the horror of the day, prosecutors compared Trump to a fire chief who delights in seeing fires spread, not extinguished, and they compared his supporters to a cavalry in war.

"This attack never would have happened, but for Donald Trump," Rep. Madeleine Dean, one of the impeachment managers, said as she choked back emotion. "And so they came, draped in Trump's flag, and used our flag, the American flag, to batter and to bludgeon." 

The Trump legal team takes the floor Friday and Saturday for up to 16 hours to lay out its defense. The difficulty facing Trump's defense became apparent at the start as his lawyers leaned on the process of the trial, unlike any other, rather than the substance of the case against the former president.

The prosecutors on Wednesday aimed to preemptively rebut arguments that Trump's lawyers have indicated are central to their defense, arguing for instance that there was no First Amendment protection for the president's encouragement of the invaders. Trump's lawyers are likely to blame the rioters themselves for the violence.

Trump is the first president to face an impeachment trial after leaving office and the first to be twice impeached. He is charged with "incitement of insurrection," though his lawyers say his words were protected by the Constitution's First Amendment and just a figure of speech.

His lawyers also say he cannot be convicted because he is already gone from the White House. Even though the Senate rejected that argument in Tuesday's vote to proceed to the trial, the legal issue could resonate with Senate Republicans eager to acquit Trump without being seen as condoning his behavior.

While six Republicans joined with Democrats to vote to proceed with the trial on Tuesday, the 56-44 vote was far from the two-thirds threshold of 67 votes needed for conviction.

Minds did not seem to be changing Wednesday, even after senators watched the graphic video.

"I've said many times that the president's rhetoric is at time overheated, but this is not a referendum on whether you agree with everything the president says or tweets," said Sen. Ted Cruz, R-Texas, who was among those leading the effort to challenge the Electoral College tally certifying the election. "This is instead a legal proceeding." 

It appears unlikely that the House prosecutors will call witnesses, and Trump has declined a request to testify. The trial is expected to continue into the weekend. 

Trump's second impeachment trial is expected to diverge from the lengthy, complicated affair of a year ago. In that case, Trump was charged with having privately pressured Ukraine to dig up dirt on Biden, then a Democratic rival for the presidency. It could be over in half the time.

The Democratic-led House impeached the president swiftly, one week after the attack.