On Thursday, the House Select Committee investigating the January 6 attack on the Capitol will reveal new evidence about Donald Trump’s last-ditch effort to pressure his vice-president, Mike Pence, to reject the electoral count, an act without historical precedent that the committee says “directly contributed” to the violent insurgency.

The panel will attempt to demonstrate how an increasingly desperate Trump became fixated on a theory devised by conservative law professor John Eastman that Pence, as Senate president, could reject congressional certification of Joe Biden’s victory in the 2020 presidential election. The vice-president does not have this authority.

The panel will argue that Trump’s embrace of this scheme – as well as his public and private pressure campaign on Pence – put the then-vice president’s life in jeopardy during the hours-long siege of Congress. It will also try to demonstrate that there is a “ongoing threat” to democracy from those who believe the 2020 election was rigged.

The panel will hear from one witness, Greg Jacob, who served as counsel to Pence when he was vice president, that Eastman’s plot to overturn the 2020 election results was illegal from the start. Despite its eventual failure, Jacob will warn that it jeopardized the American democratic experiment.

“When our elected and appointed leaders break, twist, and fail to enforce our laws in order to achieve partisan ends or to achieve frustrated policy objectives they consider existentially important, they are breaking America,” he will say in his opening remarks, which the New York Times published ahead of the hearing. “We should not pretend to be surprised when our citizens hold the law and the Constitution in the same regard that our leaders do.”

J Michael Luttig, a retired judge and informal adviser to Vice President Mike Pence, will also testify.

The committee will rely on two witnesses during the two-hour hearing on Thursday, which begins at 1pm ET, to show that Pence’s unwavering loyalty to Trump had a limit – a final request from a president refusing to accept his defeat in an election that recounts, election officials, and courts had determined was free and fair.

Squeezed between a president who refused to accept defeat and a constitution that gave him no such power to change the course of the election, the vice-president chose the constitution, according to those who advised him on Thursday.

In March, a federal judge ruled that Trump and Eastman had committed felonies in their efforts to overturn the 2020 election, including obstructing Congress’ work and conspiring to defraud the American people. The committee teased the hearing by playing a clip of former Trump White House attorney Eric Herschmann testifying that he advised Eastman to “get a great effing criminal defense lawyer – you’re going to need it.”

“What President Trump demanded of Mike Pence wasn’t just wrong; it was illegal and unconstitutional,” Wyoming Republican Congresswoman Liz Cheney, the committee’s vice-chair, said during the committee’s first primetime hearing last week.

The first session, which drew more than 20 million viewers, centered on putting Trump at the center of a sprawling “seven-part” plot to overturn an election that the committee claims he knew he lost. The second hearing examined the origins and spread of Trump’s alleged stolen election.

The hearing will be led by California congressman Pete Aguilar, a Democrat, with former US attorney John Wood, the committee’s senior investigative counsel, questioning witnesses.

Thursday’s hearing is expected to include recorded testimony from Pence’s former chief of staff, Marc Short, as well as new details about the then-vice-threats president’s of violence as an angry mob stormed the Capitol yelling “hang Mike Pence.” Nine deaths have been linked to the attack and its aftermath.

Short told CNN on the eve of the hearing that, despite the imminent danger, Pence was determined to certify the election results that night. “He knew his job was to stay at his post,” Short said.