Al Schmidt, the only Republican city commissioner to oversee the 2020 presidential election in Philadelphia, is to testify Monday before the U.S. House Select Committee to Investigate the Jan. 6 Attack on the U.S. Capitol.

Schmidt, who declined to comment about his upcoming testimony, will appear on a panel with elections attorney Benjamin Ginsberg and BJay Pak, the former U.S. attorney for the Northern District of Georgia. Then-President Donald Trump tweeted about Schmidt after the election, and the former city commissioner has said he received threats from Trump supporters who said they would murder his young children.

Also set to testify are Bill Stepien, campaign manager for Trump, and Chris Stirewalt, a former Fox News political editor who left that job amid controversy after accurately calling that Trump had lost Arizona in 2020 to Joe Biden.

Select Committee aides who requested anonymity to discuss Monday’s hearing declined on Sunday to describe specifically what they expect to hear from Schmidt and the other witnesses.

The aides described the hearing as “focused on the big lie,” Trump’s decision to spread misinformation about the 2020 election results, despite his own staff telling him that he had lost, and a long series of court rulings that debunked and rebuked those false claims.

The hearing will also examine how Trump raised “hundreds of millions of dollars” after the election and before Jan. 6 by pushing those lies, the aides said.

This won’t be Schmdit’s first trip to Washington to discuss how false claims about that election reverberated through Trump supporters.

Schmidt testified about that in October in the U.S. Senate, telling the Committee on Rules and Administration that threats to election officials increase when misinformation about those elections increases. He noted that his family received threats after the 2020 general election that died down for a time, only to increase when state legislators in Harrisburg started pushing for a so-called audit of the vote.

» READ MORE: Pa. had a starring role in the first Jan. 6 committee hearing

Schmidt has been a vocal defender of election integrity, appearing on CNN, 60 Minutes, and other television news programs to dispute false claims from Trump and others about 2020, drawing Trump’s wrath.

Trump tweeted in the weeks after the 2020 election that Schmidt “is being used big time by the Fake News Media to explain how honest things were with respect to the Election in Philadelphia. He refuses to look at the mountain of corruption & dishonesty. We win!”

That came 13 minutes after Schmidt appeared on CNN. Asked what he would tell Trump, Schmidt said: “I think people should be mindful that there are bad actors who are lying to them.”

No Republican official in Philadelphia or Pennsylvania offered support for Schmidt while Trump launched his attacks. Schmidt also said the behavior of some Trump supporters felt “very deranged.”

Schmidt announced in January 2021 that he would not seek a fourth four-year term but said his decision was not driven by the attacks from Trump and his supporters.

“That would be like capitulating to the psychological terrorists, which was their point. Or else, I’d leave today,” he told The Inquirer at the time.

» READ MORE: What we know about Mastriano’s attempts to overturn Trump’s 2020 loss in Pa.

Schmidt announced in November that he would resign in January before the end of his third term to take the helm at the Committee of Seventy, a good-government watchdog group.

Trump, who by then was banned on Twitter, sent an email to supporters about the news, calling Schmidt a “RINO” — short for “Republican in name only.”

Trump also claimed Schmidt was “a disaster on the massive election fraud and irregularities which took place in Philadelphia, one of the most corrupt election places in the United States.”

Part of Schmidt’s new job is combatting election misinformation.