The House committee investigating the January 6 insurrection said on Thursday that Donald Trump heaped immense pressure on top leaders at the justice department, engaging in a “power play to win at all costs” that nearly succeeded in overturning the will of the American people.

Testifying at the committee’s fifth and final hearing of the month, three former justice department officials, recounted a dramatic Oval Office confrontation three days before the assault on the Capitol in which Trump contemplated replacing the agency’s acting head with an “completely incompetent” lower-level official who embraced his stolen election myth. Trump only relented, they said, when he was warned that there would be mass resignations at the department if he followed through with the plan.

“For the department to insert itself into the political process this way, I think, would have had grave consequences for the country,” said Richard Donoghue, the former acting deputy attorney general, to the committee on Capitol Hill. “It may very well have spiraled us into a constitutional crisis and I wanted to make sure that he understood the gravity of the situation.”

That 3 January meeting was the culmination of a weeks-long pressure campaign by the president in which he attempted to strong arm the justice department into declaring the election corrupt.

In a breach of longstanding guidelines meant to guard the agency’s independence, Jeffrey Rosen, the former acting attorney general told the committee Trump contacted him “virtually every day” to complain that he had not done enough to investigate voter fraud in the election.

Opening the hearing, the panel’s chair, congressman Bennie Thompson, said Trump knew that the allegations of voter fraud were false, but nevertheless pressured the department to declare the election results tainted. After exhausting his legal options and being rebuffed by state and local elections officials, the panel said a desperate Trump turned to the justice department to falsely declare the election corrupt.

“Donald Trump didn’t just want the justice department to investigate,” Thompson said. “He wanted the justice department to help legitimize his lies, to basically call the election corrupt.”

In one of the near-daily conversations Trump had with the agency’s leader, Rosen told the president that the Department of Justice “can’t and won’t snap his fingers and change the outcome of an election”.

“I don’t expect you to do that,” Trump snapped back, according to Donoghue, whose handwritten notes of the exchange were displayed on a large screen during the hearing. “Just say that the election was corrupt + leave the rest to me and the [Republican] Congressmen.”

At the center of Thursday’s hearing was Jeff Clark, a department official who embraced Trump’s myth of a stolen election. At the urging of Republican congressman Scott Perry of Pennsylvania, Trump contemplated replacing Rosen with Clark, an environmental lawyer by trade.

“What was his only qualification?” congressman Adam Kinzinger, an Illinois Republican and member of the committee who led the questioning, asked rhetorically. “He would do whatever the president wanted him to do, including overthrowing a free and fair democratic election.”

Clark’s audacious effort to bend the department to Trump’s will included a draft letter addressed to state officials in Georgia falsely asserting that the department had evidence of voter fraud and suggesting the state withdraw its certification of Biden’s victory in the state. He sent the letter to Rosen and Donoghue for their signature.

Donoghue said the letter was so “extreme” and baseless he had to read it twice to grasp the gravity of what was being suggested. Both he and Rosen refused to sign it.

In a videotaped deposition, Eric Herschmann, a lawyer in the White House counsel’s office, said Clark’s plan to subvert the 2020 election was “asinine”. Using expletives, he said he told Clark: “Congratulations, you just admitted your first step or act you’d take as attorney general would be committing a felony.”

Tensions erupted on 3 January, when Clark told Rosen that Trump intended to replace him as the head of the department. White House call logs from that afternoon showed that the White House staff was already referring to Clark as the “acting attorney general”, the committee showed.

Rosen, refusing to be fired by a subordinate, demanded a White House meeting. That night, Rosen, Donoghue, and Steven Engel, the former assistant attorney general for the office of legal counsel, who also testified on Thursday, gathered in the Oval Office with Trump and top White House lawyers for a tense, hours-long meeting.

Donoghue said Trump appeared ready to follow through with the plan to replace Rosen with someone who promised fealty. “What have I got to lose?” Donoghue recalled Trump saying. “A lot,” he replied. He and Engel walked Trump through the implications of such a dramatic shift, warning him that there would be mass resignations among senior officials. Donoghue said Engel told the president Clark would be “leading a graveyard”.

“It was very strongly worded to the president that that would happen,” Donoghue said.

Their warnings were ultimately persuasive and Trump relented. Before they left, Donoghue said Trump asked him what would happen to Clark. He explained that only Trump could fire him. Trump replied that he wouldn’t.

The panel also revealed that several of Trump’s allies in Congress had requested pardons from the president in the days after the deadly assault on the Capitol. It displayed an email from congressman Mo Brooks in which the Alabama Republican asked the White House to consider a presidential pardon for himself and other congressional allies.

In testimony, Trump aides said Republican congressmen Scott Perry of Pennsylvania; Matt Gaetz of Florida; Louie Gohmert of Texas and Andy Biggs of Arizona all requested “pre-emptive” pardons. All voted against certifying the results of the election in the hours after the riot.

“The only reason I know to ask for a pardon is because you think you’ve committed a crime,” Kinzinger said.

The panel voted unanimously to hold Clark in contempt of Congress after he failed to cooperate with its investigation. He later appeared before the committee but Kinzinger said he asserted his fifth amendment right against self-incrimination more than 125 times.

Just before the hearing began, it was revealed that federal investigators searched Clark’s home earlier this week, according to a person familiar with the matter who was not authorized to speak publicly.

In new testimony from the committee’s taped deposition with Bill Barr, the former attorney general, said he thought it was important for the department to investigate – and ultimately disprove – Trump’s false claims of voter fraud. Had it not, Barr said he shuddered to think what might have happened. “I’m not sure we would have had a transition at all.”

The officials’ testimony on Thursday all bolstered Barr’s conclusion that the president’s claims of election fraud were “bullshit”. Among the outlandish claims Trump latched onto was a purported plot involving an Italian defense contractor who purportedly conspired with US intelligence to manipulate the vote count. In an email to Rosen, Donoghue called the conspiracy “pure insanity”.

The committee is building the case that Trump was at the heart of the sprawling conspiracy that led to the violence on January 6 – a lie that has only metastasized in the months since a pro-Trump mob stormed the Capitol with pipes, bear spray and Confederate flags. Nine people died in the assault and its aftermath.

The committee said it would resume public hearings in July as part of its efforts to reveal in serial fashion what Thompson described as the “inner workings of what essentially was a political coup”.

Future sessions are expected to detail how extremist groups like the Proud Boys planned the attack on Congress and how Trump failed to act to stop the violence once it erupted on 6 January.

Concluding Thursday’s hearing, Kinzinger, one of Trump’s few Republican critics who is retiring at the end of his term, said Trump “was willing to sacrifice our republic to prolong his presidency”. He came close, Kinzinger said, but ultimately failed thanks to the “good people” who put their oath of office first.

But, he warned: “I’m still worried that not enough has changed to prevent this from happening again.”