Jan. 6 committee to detail how Trump and allies tried to coerce Pence

The pressure campaign on Vice President Mike Pence to help overturn the election -- before and on the day of the Capitol attack -- is the subject of the next Jan. 6 committee hearing Thursday.

The committee says it will detail what it calls the plot by then-President Donald Trump and his allies -- with coercing Pence to go along being a desperate last effort to accomplish their goal.

In a preview, aides said the hearing will focus on the theory that Pence could unilaterally reject electors on Jan. 6 as Congress met to certify the 2020 election results, then on the campaign against Pence by Trump in private and public -- even as White House aides were saying -- and telling Trump -- the scheme was illegal.

The committee intends to show, they said, how "that pressure campaign directly contributed to the attack on the Capitol" and put Pence's life at risk, as well as what aides described as the ongoing threat to democracy because many Americans continue to believe Trump's false claims of election fraud.

It's expected Americans tuning in at 1 p.m. ET will hear from former Pence chief of staff Marc Short via pre-recorded video testimony, along with others who have testified behind closed doors.

Testifying live will be Pence's former counsel, Greg Jacob, and retired federal judge J. Michael Luttig, who advised Pence informally.

Rep. Pete Aguilar, D-Calif., will lead leading the questioning after opening statements from Chairman Bennie Thompson, D-Miss., and Vice Chair Liz Cheney, R-Wyo.

"President Trump had no factual basis for what he was doing and he had been told it was illegal," Cheney said in a video teasing Thursday's hearing. "Despite this, President Trump plotted with a lawyer named John Eastman and others to overturn the outcome of the election on Jan. 6."

The committee promised viewers will see "new materials" that document where former Pence was and what he was doing on Jan. 6

On Wednesday night, ABC News published exclusively obtained photos of Pence on Jan. 6, including one showing him and his family hiding in the vice-president's ceremonial office after being whisked off the Senate floor as the mob attacked.

Pence's wife Karen can be seen closing the curtains to make sure the rioters -- some chanting "Hang Mike Pence" -- couldn't see inside.

Pence later tweeted photos of him hiding in a parking garage in the Capitol complex before he eventually returned to preside over the certification of Joe Biden's victory.

ABC News' Katherine Faulders and Benjamin Siegel contributed to this report.