In videotaped testimony, Barr dismissed Trump’s claims of fraud.

Representative Bennie Thompson, Democrat of Mississippi, opened the hearing by calling the actions of former President Donald J. Trump an “attempted coup,” laying out starkly the threat that the country faced on Jan. 6, 2021.

A clip was shown of the testimony of Bill Barr, Mr. Trump’s last Senate-confirmed attorney general, in which Mr. Barr dismissed Mr. Trump’s repeated claims of fraud and recalled how he had told the president he considered it “bullshit” and wanted no part of it.

Mr. Thompson went on to describe the ongoing threat to democracy from the anger that Mr. Trump fomented ahead of that day.

Finally, Representative Liz Cheney described testimony that will be played showing that Mr. Trump cheered on the rioters as they were swarming the building, including telling his aides that perhaps Vice President Mike Pence “deserved” to be hanged, as the rioters demanded.

All the testimony has added up to show how Mr. Trump was trying to “destroy” the U.S. government, Ms. Cheney said.