A White House aide testified that Trump ordered security lifted on Jan. 6 though the crowd was heavily armed.

WASHINGTON — Former President Donald J. Trump knew the crowd he amassed in Washington on Jan. 6, 2021, was armed and could turn violent, but wanted security precautions lifted because he said his supporters were not there to attack him, according to a junior White House aide who testified on Tuesday to the House committee investigating the attack.

In extraordinary blow-by-blow testimony based on episodes she witnessed in the West Wing of the White House, Cassidy Hutchinson, an aide to Mark Meadows, the former chief of staff, revealed that the president had demanded to march to the Capitol with his supporters even as the riot was underway, at one point trying to grab the steering wheel of the presidential limo from a Secret Service agent when he was told he could not go.

Among the other revelations the committee presented on Tuesday:

• Ms. Hutchinson testified that Mr. Trump demanded that his supporters be able to move around freely even though he knew they were armed, objecting to the presence of magnometers to detect weapons. She testified that she was “in the vicinity of a conversation where I overheard the president say something to the effect of, ‘You know, I don’t f-ing care that they have weapons. They’re not here to hurt me. Take the f-ing mags away. Let my people in. They can march to the Capitol from here. Let the people in. Take the f-ing mags away.’”

• As rioters stormed the Capitol, chanting “Hang Mike Pence,” Mr. Trump endorsed the violence. Ms. Hutchinson testified that Mr. Meadows said of Mr. Trump, “He doesn’t want to do anything,” and “He thinks Mike deserves it. He doesn’t think they’re doing anything wrong.”

• Ms. Hutchinson testified that Mr. Meadows was worried as early as Jan. 2 that Mr. Trump’s rally could get out of control, telling her “Things might get, real, real bad on Jan. 6.” Rudolph W. Giuliani had told her it would be a great day, when Mr. Trump would go to the Capitol and be with members of Congress.

• Anthony M. Ornato, the former White House chief of operations, warned Mr. Meadows on Jan. 6 that the crowd seemed ready for violence, and had knives, guns, bear spray, body armor, spears and flagpoles. She said Mr. Meadows did not look up from his phone, but asked Mr. Ornato whether he had informed Mr. Trump, which Mr. Ornato said he had. “He almost had a lack of reaction,” Ms. Hutchinson testified of Mr. Meadows’ reaction to the mob attacking the Capitol.

• Ms. Hutchinson testified that there had been discussions about Mr. Trump giving a speech at the Capitol on Jan. 6 and even going into the House chamber as Congress met to make its official count of electoral votes. But Pat Cipollone, the White House counsel, had serious legal concerns about Trump marching to the Capitol on Jan. 6, Ms. Hutchinson testified, saying that he had told her: “We’re going to get charged with every crime imaginable.”

• Ms. Hutchinson said she was outraged that Mr. Trump continued to tweet against Mr. Pence as the violence raged at the Capitol, denigrating him even as the crowd was braying for his execution. “As an American, I was disgusted. It was unpatriotic. It was un-American. We were watching the Capitol building get defaced over a lie,” she said.

• Inside the White House, Mr. Trump became enraged when he learned that William P. Barr, the former attorney general, had publicly shot down his false allegations of a stolen election. He beat the table and threw dishes, splattering ketchup on the wall, Ms. Hutchinson said, adding that it was not the first time she had seen the president smash crockery in a rage.