WASHINGTON — Federal agents searched a former top Justice Department official’s home and seized records from key Republicans in at least five states linked to President Trump’s efforts to overturn the 2020 election, signaling that authorities are ramping up their investigation of associates of the former president.

Authorities on Wednesday searched the Virginia home of Jeffrey Clark, who was known at the Justice Department to champion Mr. Trump’s claims of election fraud. 

Agents in recent days also served subpoenas on the Republican Party chairmen of Arizona, Nevada and Georgia, three states that went for President Biden and where Mr. Trump’s allies created slates of “alternate electors” intended to subvert the vote. And Republicans in two other states — Michigan and Pennsylvania — disclosed they had been interviewed by the FBI.

The Justice Department appears to be escalating its probe of pro-Trump efforts to overturn the 2020 election, which culminated in the deadly January 6 Capitol attack. 

The disclosures of law enforcement activity came as the House committee investigating the riot said it had new evidence of Mr. Trump’s efforts and his knowledge that he had no legal basis to try to overturn the election.

The committee’s Thursday hearing focused on Mr. Trump’s desire to install Mr. Clark atop the Justice Department in his administration’s last days. The reason for the search of Mr. Clark’s home was not immediately clear and it was not known what information agents were searching for. 

The person who confirmed the search was not authorized to discuss it by name and spoke on condition of anonymity.

In an interview Thursday night on Fox News Channel, Mr. Clark alleged the timing of the search warrant was “highly politicized” and questioned why his home was searched one day before the congressional hearing.

“It looks highly coincidental and … I just don’t believe in coincidences,” he said.

Both the committee and federal authorities are probing the use of replacements for duly chosen electors in seven battleground states that voted for Mr. Biden. Mr. Trump and his allies furiously pressured authorities in those states to replace Mr. Biden’s electors with ones for him on specious or nonexistent allegations that his victory was stolen.

The committee this week disclosed text messages that showed an aide to Senator Johnson, a Wisconsin Republican and Trump ally, tried to hand-deliver fake elector certificates to an aide of Vice President Pence. The texts show Mr. Pence’s aide refused to accept the votes.

Mr. Johnson told a Wisconsin conservative talk radio host on Thursday that the fake elector slates came from the office of Representative Mike Kelly of Pennsylvania. A spokesman for Mr. Kelly responded that Mr. Johnson’s claim was “patently false.”

The spokesman, Matt Knoedler, said “Mr. Kelly has not spoken to Senator Johnson for the better part of a decade, and he has no knowledge of the claims Mr. Johnson is making related to the 2020 election.”

Among those who have received subpoenas in recent days, according to a person familiar with the matter who was not authorized to discuss an ongoing investigation, was Georgia’s Republican Party chairman, David Shafer.

The Nevada GOP chairman, Michael McDonald, turned over his phone to federal agents Wednesday when they approached him outside his car in Las Vegas and presented a warrant, according to another person familiar with the matter. 

Mr. McDonald in December 2020 stood outside Nevada’s state capitol with other fake electors to swear a so-called “oath of office,” flanked by men in camouflage with semi-automatic rifles.

The Arizona Republican Party chairwoman, Kelli Ward, her husband, Michael Ward, and two other alternate electors also received subpoenas, according to a third person familiar with the matter who was not authorized to discuss it publicly.

In Pennsylvania, FBI agents interviewed the chairman of the Allegheny County Republican Party at his home Thursday and gave him a subpoena for communications between him, Trump electors in the state and members of Mr. Trump’s campaign and legal team, the party official, Sam DeMarco, told the Pittsburgh Post-Gazette.

Mr. DeMarco said in a statement that his conduct as an elector was “open, above-board and predicated solely on protecting President Trump’s legal rights should he prevail in court. That is why I agreed to serve as an elector solely in the event the president prevailed in his legal challenge to the Pennsylvania vote.”

And in Michigan, Michele Lundgren told the Detroit News that someone from the FBI served her with a subpoena Thursday and that another Trump elector was served on Wednesday. 

Ms. Lundgren, 72, said her discussion with the agent was “long” and “pleasant” and that she let one of the agents go through her phone and computer.

“They kept asking me questions and asking me questions, and I kept telling them answers,” she said.

Mr. Clark’s home was searched by federal agents shortly before a committee hearing in which he was the focus. Three other former Justice Department officials testified about an extraordinary January 3, 2021, Oval Office meeting at which Mr. Trump contemplated naming Mr. Clark — who led the department’s civil division — as acting attorney general in place of Jeffrey Rosen, who resisted Mr. Trump’s efforts to involve the agency.

Mr. Trump relented only when other senior Justice Department officials warned Mr. Trump that they would resign if he followed through with his plan to replace Mr. Rosen with Mr. Clark.

A lawyer for Mr. Clark did not return an e-mail and phone message seeking comment.

The chairman of the January 6 committee, Representative Bennie Thompson, said he read about the raid on Clark’s home moments before the hearing started. 

“We’re not privy to what the Department of Justice’s reasoning is for doing it,” he said. “As you know, we demonstrated that he was recommended to lead the Department of Justice and people felt that he was absolutely unqualified to do so.”

Mr. Clark recently joined the Center for Renewing America as a senior fellow. The president of the center, Russ Vought, tweeted that federal officers forced Mr. Clark “into the streets” while he was wearing pajamas and “took his electronic devices.”

“All because Jeff saw fit to investigate voter fraud,” Mr. Vought continued. “This is not America, folks. The weaponization of govt must end. Let me be very clear. We stand by Jeff and so must all patriots in this country.”