Jan. 6 hearing witness: Irate Trump grabbed wheel, demanded to go to Capitol

Chair Bennie Thompson, D-Miss., convened the unexpected hearing shortly after 1 p.m. with Cassidy Hutchinson, a former top aide to Trump White House chief of staff Mark Meadows, taking her seat as members took the dais.

In brief opening remarks, he explained information that she had needed to be shared with the American people "immediately" and hailed her courage.

"In recent days, the select committee has obtained new information, dealing with what was going on in the White House on Jan. 6, and in the days prior. Specific, detailed information about what the former president and his top aides were doing and saying in those critical hours. Firsthand details of what transpired in the Office of the White House chief of staff," Thompson said.

"It hasn't always been easy to get that information, because the same people who drove the former president's pressure campaign to overturn the election are now trying to cover up the truth about January 6. But thanks to the courage of certain individuals, the truth won't be buried. The American people won't be left in the dark," he added. "Our witness today is Cassidy Hutchinson, she has embodied that courage."

With the nature of the hearing coming up with little notice, signaling urgency for the committee, reporters and cameras swarmed the witness table inside the Cannon Office Building ahead of Cassidy Hutchinson taking her seat.

Hutchinson entered the hearing room at 1 p.m. with members of the Jan. 6 committee.

ABC News Chief Washington Correspondent Jon Karl said sources have told him the hearing will be "Big —and disturbing."

Former White House deputy press secretary Sarah Matthews showed support for Cassidy Hutchinson ahead of her scheduled testimony.

"Just want to say how much admiration I have for the tremendous bravery Cassidy Hutchinson is displaying," Matthews wrote on Twitter. "Even in the face of harassment and threats, she is choosing to put her country first and tell the truth."

"This is what real courage, integrity, and patriotism looks like," Matthews added.

Matthews resigned from her position in the Trump administration on Jan. 6 , stating she was "deeply disturbed" by what took place that day.

Cassidy Hutchinson hired a new attorney, Jody Hunt, earlier this month to represent her as the public Jan. 6 hearings began. Her agreement to testify publicly comes after months of negotiations between the committee and her counsel, sources told ABC News.

At the start of the Trump administration, Hunt served as chief of staff to then-Attorney General Jeff Sessions. He later became the head of the Department of Justice's Civil Division.