WASHINGTON — The House Select Committee to Investigate the Jan. 6 Attack on the United States Capitol opened a landmark set of hearings on Thursday by showing video of aide after aide to former President Donald J. Trump testifying that his claims of a stolen election were false, as the panel laid out in meticulous detail the extent of the former president’s efforts to keep himself in office.

Over about two hours, the panel offered new information about what it characterized as an attempted coup orchestrated by Mr. Trump that culminated in the deadly assault on the Capitol. The panel’s leaders revealed that investigators heard testimony that Mr. Trump endorsed the hanging of his own vice president as a mob of his supporters descended on Congress. They also said they had evidence that members of Mr. Trump’s cabinet discussed invoking the 25th Amendment to remove him from office.