Top advisers to then-president Trump told him that his claims of widespread election fraud were not legitimate and would not reverse his election loss, according to video testimony aired on Monday by the committee investigating the January 6th, 2021, riot at the US Capitol.
The Democratic-led House of Representatives panel made the case that Mr Trump decided to claim that the 2020 presidential election was "stolen" from him even though many of his staffers said that Democrat Joe Biden had won more votes.
"He and his closest advisors knew those claims were false, but they continued to peddle them anyway, right up until the moments before a mob of Trump supporters attacked the Capitol," Democratic Representative Zoe Lofgren told the panel in its second hearing.
In video testimony, Mr Trump's former Attorney General William Barr bluntly dismissed claims of fraud as "bullshit" and "crazy stuff."
"If he really believes this stuff, he's become detached from reality," Barr said.
'Witchhunt'
Mr Trump has denied wrongdoing, and has repeatedly insisted that he did not lose, dismissing the Select Committee investigation as a political witchhunt.
The hearing was delayed for about 45 minutes after William Stepien, Mr Trump's campaign manager in the final few months of the White House race, pulled out at the last minute, citing a family emergency as his wife went into labour.
The committee aired video footage of Mr Stepien's testimony to investigators instead, along with footage from other close Trump aides - including his daughter Ivanka - describing events on Election Day when Mr Trump was told that it was too early to declare victory.
"It was becoming clear that the race would not be called on election night," Ivanka Trump said.
Mr Stepien said his recommendation was for Mr Trump to say votes were still being counted, it was too early to call the election, but he was proud of the race he had run.
Matthew Morgan, chief lawyer of Mr Trump's campaign, said in video testimony that any claims of fraud would not change the outcome of election.
'No legitimate argument'
The panel is holding the hearings to discuss initial findings of its nearly year-long investigation into the events of Janiary 6th, when thousands of Trump supporters attacked the Capitol as vice president Mike Pence and lawmakers met to certify Mr Biden's victory.
"The Trump campaign legal team knew there was no legitimate argument for fraud, irregularities or anything to overturn the election," Republican Representative Liz Cheney, the panel's vice chairperson, said.
Monday's session followed a blockbuster hearing on Thursday night featuring testimony showing that close Trump allies - even Ivanka - rejected his false claims of voting fraud. Nearly 20 million Americans watched the unusual hearing aired in the primetime peak television viewing hours.
Mr Trump has denied wrongdoing and he and his supporters dismiss the Democratic-led Select Committee as a political witchhunt. Democrats call it a necessary investigation into a terrible and deadly event and say House of Representatives Speaker Nancy Pelosi wanted a bipartisan independent commission but Republicans refused.
Chris Stirewalt, a former political editor at Fox News, described the network's early call that Mr Trump had lost the swing state of Arizona, which witnesses said angered Trump's team.
Witnesses scheduled to testify in the hearing room later on Monday included conservative Republican election attorney Ben Ginsberg, Byung J. "BJay" Pak, who resigned as U.S. attorney in Atlanta as Trump's camp questioned Georgia's election results, and Al Schmidt, the only Republican on Philadelphia's elections board who became a target of attacks after he defended the integrity of the 2020 vote.
Georgia and Pennsylvania were among states that backed Mr Trump in the 2016 election, but went for Mr Biden in 2020. They have been a focus of the unfounded assertions of election fraud.
Four people died the day of the attack, one fatally shot by police and the others of natural causes. Some 140 police officers were injured, and one died the next day. Four officers later died by suicide.
Nearly 850 people have been arrested for crimes related to the riot, including more than 250 charged with assaulting or impeding law enforcement.
