House Minority Leader Kevin McCarthy, R-Calif., wouldn’t say Thursday if President Joe Biden was the legitimate winner of the 2020 election.

ABC News Chief Washington Correspondent Jonathan Karl pressed McCarthy on the matter four times during a news conference where House Republicans preemptively slammed tonight’s hearing, calling the Jan. 6 panel "the most political and least legitimate committee in American history."

McCarthy said Biden is the president, but declined to address the legitimacy aspect and declined to say Trump was wrong when he baselessly claimed the election was fraudulent.

The select committee has promised never-before-seen videotaped depositions from some of Trump's closest aides and family members after Ivanka Trump, Jared Kushner and Donald Trump Jr. all sat for interviews earlier this year.

Former White House chief of staff Mark Meadows -- who turned over thousands of text messages to the committee -- has been described by congressional sources as an "MVP" of the hearings, as his messages have provided somewhat of a roadmap for investigators.

Click here for some key players to watch for as the panel kicks off a series of major public hearings.

President Joe Biden said a lot of Americans will learn new details about the Jan. 6 attack as lawmakers begin to reveal the findings of their 11-month investigation.

"One of the things that’s gonna occupy my country tonight, I suspect, is the first open hearings on January the 6th," Biden said as he sat down with Canadian Prime Minister Justin Trudeau at the Summit of the Americas on Thursday afternoon.

"And as I said when it was occurring and subsequent, I think it was a clear, flagrant violation of the Constitution," Biden continued. "I think these guys and women broke the law, tried to turn around the result of an election. And there's a lot of questions: who's responsible, who's involved?"

Thursday's hearing, the first of six scheduled in June, is the culmination of an 11-month-long investigation by the House select committee.

The nine-member panel has collected more than 140,000 documents and 1,000 witness interviews throughout the course of the investigation, and members have promised to introduce never-before-seen videos and exhibits they say will shock the public.

ABC News Television Network will air special coverage of the hearing at 8 p.m. and ABC News Live will carry gavel-to-gavel coverage.

The committee aired a video showing the moment Capitol Police officer Caroline Edwards was knocked out as she tried to hold the line from a crowd of rioters pushing up against barricades and bike racks.

Edwards winced as the video began.

"I felt the bike rack come on top of my head and I was pushed backwards, and my foot caught the stair behind me, and my chin hit the handrail," she said. "At that point I blacked out but the back of my head clipped the concrete stairs behind me."

Edwards returned to duty after regaining consciousness, saying "adrenaline kicked in" as she went to the West Front of the Capitol to protect the Senate steps. There she helped people who had gotten pepper sprayed and others injured before she was hit herself with pepper spray and tear gas.