Jan. 6 hearing told Trump knew plan to pressure Pence was illegal, went ahead anyway

Greg Jacob, a former adviser to Pence, said they analyzed history and constitutional text to map out the vice president’s role when it came to certifying elections.

The two then examined “every single electoral vote count that had happened in Congress” since the country’s founding, Jacob testified. They found no vice president ever claimed to have the kind of authority Trump and his attorney John Eastman claimed Pence had.

“The history was absolutely decisive and again, part of my discussion with Mr. Eastman was, ‘If you were right, don't you think Al Gore might have liked to have known in 2000 that he had authority to just declare himself president of the United States? Did you think that the Democrat lawyers just didn't think of this very obvious quirk that he could use to do that?'”

Trump and Pence haven't spoken to one another since last summer, according to sources familiar with their conversations.

Pence defended Trump through a slate of controversies during their administration. But, as the House committee is highlighting at its hearings, Pence drew a line at Trump's alleged plot to overturn the election -- breaking from the president and drawing the rage of the Trump mob on Jan. 6.

When ABC News Chief Washington Correspondent Jonathan Karl interviewed Trump for his book "Betrayal," Karl asked about the "Hang Mike Pence" chants and whether Trump had been concerned for the safety of the man he chose to be his vice president.

“Well, the people were very angry,” Trump said.

“They said, ‘hang Mike Pence,’” Karl told Trump.

“It’s common sense, Jon. It’s common sense that you’re supposed to protect,” Trump said. “How can you, if you know a vote is fraudulent, right, how can you pass on a fraudulent vote to Congress?”

While Pence himself isn't testifying and has not sat before the committee, a range of former Pence aides cooperated with the investigation.

Since his term ended, Pence has publicly reiterated he had no power to overturn the 2020 results. But like other conservatives, he has said "election integrity" should be a national priority.

-ABC News' Katherine Faulders

Notable faces were spotted across the hearing room as proceedings kicked off Thursday.

Capitol Police Officer Harry Dunn, Capitol Police Staff Sgt. Aquilino Gonell, Metropolitan Police Officer Daniel Hodges and former Metropolitan Police Officer Michael Fanone, who testified at the committee's first hearing last year on their experience defending the Capitol on Jan. 6, were all present.

Former Pence national security adviser Olivia Troye, who resigned from the administration in 2020, was spotted sitting next to Gonell as well as Allison Gill, a former high-level Veterans Affairs official who was secretly recording a podcast on the weekends about Robert Mueller's investigation that attracted thousands of listeners.

A couple of members of Congress have been spotted in the back of the room including Reps. Ayanna Pressley, D-Mass., and Steve Cohen, D-Tenn., sitting together. Rep. Adam Kinzinger, R-Ill., who along with Vice Chair Liz Cheney has been ostracized by the Republican Party for speaking out against Trump, also stopped by.

-ABC News' Katherine Faulders and Benjamin Siegel

In his testimony on Thursday, former federal judge Michael Luttig painted a dire picture of what he believed would have happened had Pence followed through with Trump’s plea to remain in power.

“That declaration of Donald Trump as the next president would have plunged America into what I believe would’ve been tantamount to a revolution within a constitutional crisis in America,” Luttig said, “which in my view, and I am only one man, would’ve been the first constitutional crisis since the founding of the republic.”

Luttig is one of the panel's two live witnesses in today's hearing. The former judge informally advised Pence on his role in affirming the results of the 2020 presidential election.