In explosive public testimony, a former White House aide told the January 6 committee Donald Trump knowingly directed armed supporters to march to the US Capitol in a last-gasp effort to overturn the 2020 presidential election.

Appearing at a hastily scheduled hearing, Cassidy Hutchinson, a former aide to Trump’s final chief of staff, Mark Meadows, painted a devastating portrait of a raging president spiraling out of control and a White House often too ambivalent to stop him.

Hutchinson also offered stunning new details that Trump and key aides were aware that a rally on 6 January 2021 could turn violent days before Trump urged supporters to “fight like hell” to keep him in power.

“Things might get real, real bad on 6 January,” Hutchinson recalled Meadows telling her on 2 January.

“That evening was the first moment that I remember feeling scared and nervous about what could happen on January 6,” she said.

The hearing concluded with another extraordinary disclosure: the committee vice-chair, Liz Cheney, suggested Trump allies have sought to “influence or impact” witnesses.

“I think most Americans know that attempting to influence witnesses to testify untruthfully presents very serious concerns,” Cheney said, adding that the committee was “carefully considering our next steps”.

Over nearly two hours, Hutchinson offered a shocking view into the West Wing before, during and after the Capitol attack. In gripping detail, she described Trump throwing his lunch against the wall, lunging for a secret service agent’s throat and insisting armed supporters be allowed entrance to the rally that preceded the riot.

“I felt like I was watching a bad car accident about to happen, where you cannot stop it,” said Hutchinson, a conservative Republican who worked just steps from the Oval Office.

On the morning of 6 January, Hutchinson was present for a briefing with Meadows in which they were informed by Tony Ornato, the deputy chief of staff, that members of the crowd in Washington were carrying knives, guns, rifles, bear spray, body armor and spears. Asked if Trump had been briefed, Meadows affirmed that he had.

When they arrived at the Ellipse, Hutchinson said, Trump was furious that the crowd was not at capacity and demanded Secret Service loosen security precautions to let in supporters who did not want to go through metal detectors. She recalled overhearing him say, “They’re not here to hurt me.”

Back at the White House, she recalled a disturbing conversation with Ornato, who rode in the presidential limousine with Trump after his remarks. Ornato told her Trump became “irate” when told he would return to the White House instead of going to the Capitol. Hutchinson testified that Trump told a Secret Service agent: “I’m the effing president, take me up to the Capitol now.”

When the agent said he could not, Trump lunged for the steering wheel and when that failed, grabbed at the agent’s throat, she said. She said the agent, Robert Engel, was present when Ornato described the altercation to Hutchinson and did not dispute his account.

Trump was so enraged that he threw his lunch at the wall. It wasn’t the first time Hutchinson had witnessed such an outburst. Weeks before, Trump threw his lunch against the wall after his attorney general, William Barr, said the president’s claims of a stolen election were without merit.

“There was ketchup dripping down the wall, and there was a shattered porcelain plate on the floor,” Hutchinson recalled.

As Trump’s supporters inched closer to the Capitol on 6 January, Hutchinson said she sought to sound the alarm at the White House. But instead of seeking to calm the situation, Trump sent a tweet saying Mike Pence lacked the “courage” to stop the electoral count.

“As an American, I was disgusted,” Hutchinson said. “It was unpatriotic. It was un-American. We were watching the Capitol building get defaced over a lie.”

Capitol police officers engaged in hand-to-hand combat, trying to stop the mob as lawmakers and the vice-president were rushed to safety. An early hearing revealed that the rioters chanting “hang Mike Pence” had come with 40ft of him. Trump refused to condemn the violence or issue a statement urging supporters to go home. He even expressed approval of the chants about Pence, Hutchinson said.

Pat Cipollone, the former White House counsel, implored Meadows to “do more” to stop the violence, saying: “They’re literally calling for the vice-president to be effing hung.”

“You heard him, Pat,” Meadows replied. “He thinks Mike deserves it. He doesn’t think they are doing anything wrong.”

Having said it would next hold hearings in July, the committee scheduled Hutchinson’s appearance abruptly. Opening the hearing, the committee chair, Bennie Thompson, said it was “important that the American people hear that information immediately”.

Trump sought to discredit Hutchinson on his social media platform, calling her a “phony” and a “bullshit artist”. But former Trump aides who broke with him over January 6 praised her courage.

Few Trump loyalists were left unscathed by Tuesday’s hearing, including Michael Flynn, the former national security adviser.

The committee played a montage of Flynn invoking his Fifth Amendment right against self-incrimination. In one revealing exchange, the retired general declined to answer when asked if he believed in the peaceful transfer of power.

The committee had previously relied on Hutchinson’s testimony to reveal that several far-right members of Congress who attempted to stop certification of Biden’s victory sought pardons after the attack.

On Tuesday, Hutchinson recalled walking Trump’s lawyer, Rudy Giuliani, to his car on the evening of 2 January. He told her Trump was planning to be with his allies on Capitol Hill during the certification. When she reported this to Meadows, she said he replied something to the effect of: “Things might get real, real bad on January 6.”

She also told the committee she recalled mentions of the far-right groups the Oath Keepers and the Proud Boys when Giuliani was around at the White House in the days leading up to January 6.

Hutchinson said Meadows and Giuliani sought presidential pardons. She also told the committee members of Trump’s cabinet discussed invoking the 25th amendment, which allows for the forced removal of a president.

Tuesday’s hearing came as a surprise but the committee has said its public sessions are prompting more witnesses to come forward, helping uncover new evidence about what Thompson said was the “culmination of an attempted coup”.

In its episodic presentation, the committee has made use of recorded depositions, blending tapes with moving public testimony and dramatic speech-making from lawmakers and staff.

At least two more hearings are expected next month, to explore how far-right and paramilitary groups organized and prepared for the January 6 attack and Trump’s abdication of leadership during the hours-long siege of the Capitol.

The panel’s leaders praised Hutchinson for not taking the “easy course” and remaining silent. Cheney urged others who have so far declined to speak to the panel, Cipollone among them, to follow Hutchinson’s example.

“Our nation is preserved by those who abide by their oaths to our constitution,” she said in closing. “Our nation is preserved by those who know the fundamental difference between right and wrong.”