Donald Trump deluged aides with wild voter fraud conspiracy theories after losing the 2020 US election, his top law-enforcement official said in testimony revealed Monday by a congressional probe which the ex-president branded a "mockery of justice."

Appearing in a pre-recorded deposition at a congressional hearing into the 2021 assault on the US Capitol, former attorney general Bill Barr described his then-boss as having no interest in the facts that debunked his groundless narrative.

"I was demoralized because I thought, boy... he's become detached from reality if he really believes this stuff," Barr told the House committee investigating the January 6 insurrection by supporters of Trump.

"When I went into this and would tell him how crazy some of these allegations were, there was never an indication of interest in the actual facts," said Barr, who likened addressing Trump's avalanche of false allegations with playing the game "whack-a-mole."

Former US president Donald Trump prematurely and falsely declared victory on election night on November 4, 2020
Former US president Donald Trump prematurely and falsely declared victory on election night on November 4, 2020 GETTY IMAGES NORTH AMERICA via AFP / Drew Angerer

The panel is holding six hearings throughout June to outline its case that the riot at the seat of US democracy in Washington was the culmination of a seven-step conspiracy by Trump and his inner circle to overturn his defeat to Joe Biden.

Trump ignored repeated warnings from top aides against falsely claiming the November 2020 election was stolen, according to testimony unveiled by the panel.

"We will tell the story of how Donald Trump lost the election -- and knew he lost the election -- and as a result of his loss, decided to wage an attack on our democracy," the committee's Democratic chairman Bennie Thompson said in his opening remarks.

Trump released his first extended reaction to the probe Monday evening, with a rambling 12-page statement in which he called the panel a "mockery of justice" and a "Kangaroo Court hoping to distract the American people from the great pain they are experiencing."

The second of six planned hearings was shown videotaped accounts from the former president's advisors, including Barr and campaign manager Bill Stepien, saying they repeatedly counseled him not to declare victory on election night because he hadn't won -- but that Trump went ahead anyway.

The House panel probing the US Capitol riot holds its second public hearing in Washington on June 13, 2022
The House panel probing the US Capitol riot holds its second public hearing in Washington on June 13, 2022 POOL via AFP / Jabin Botsford

"He thought I was wrong, he told me so, and that they were going to go in a different direction," Stepien said.

Thompson's deputy on the panel, Republican lawmaker Liz Cheney, said Trump chose to listen to the advice of "apparently inebriated" former New York mayor Rudy Giuliani "to just claim he won, and insist that the vote counting stop -- to falsely claim everything was fraudulent."

Trump started pushing what came to be known as his "Big Lie" around 2:30 am on November 4, 2020, prematurely declaring victory on the night of an election he ultimately lost to Biden by seven million votes.

Former US president Donald Trump prematurely and falsely declared victory on election night on November 4, 2020
Former US president Donald Trump prematurely and falsely declared victory on election night on November 4, 2020 GETTY IMAGES NORTH AMERICA via AFP / Drew Angerer

Barr said in his testimony that Trump claimed major fraud "right out of the box on election night... before there was actually any potential of looking at evidence."

Giuliani and associates including the lawyer Sidney Powell would go on to push debunked theories of massive voter fraud that put them at odds with the White House lawyers Stepien referred to as "Team Normal."

Cheney highlighted "far-flung conspiracies" -- dismissed as "nonsense" by Barr -- of fraud involving voting machines "with a deceased Venezuelan Communist allegedly pulling the strings."

Trump repeated a number of unfounded claims in his statement late Monday.

"Democrats created the narrative of January 6th to detract from the much larger and more important truth that the 2020 Election was Rigged and Stolen," he said.

The committee says the initial claim of fraud grew quickly into a conspiracy to cling to power by Trump and his inner circle -- and a fundraising campaign that raised $250 million between election night and the Capitol insurrection.

The committee's senior investigative counsel Amanda Wick said much of the cash was funneled into a political action committee that made donations to pro-Trump organizations.

"As early as April 2020, Mr Trump claimed that the only way he could lose an election would be as a result of fraud," Democratic panel member Zoe Lofgren said.

"The big lie was also a big rip-off," she said, promising to show how the Trump campaign raised hundreds of millions of dollars from supporters who were falsely led to believe their donations would be used for the legal fight over fraud claims.

All but one of the 62 lawsuits filed by the Trump campaign were dismissed -- the vast majority by Republican-appointed judges -- while the one that was upheld didn't affect the outcome.

Powell filed four federal lawsuits in staunchly Democratic cities that were all rejected as frivolous and, in Detroit, a judge ordered that she face sanctions for a "historic and profound abuse of the judicial process."

The panel ended the hearing by returning to the Capitol riot, showing footage of mob participants explaining how Trump's voter fraud claims had motivated their actions.

"I know exactly what's going on right now. Fake election," one said.