WASHINGTON — The House committee investigating the Jan. 6 attack on the Capitol on Thursday asked former Speaker Newt Gingrich to sit for a voluntary interview about his involvement in former President Donald J. Trump’s effort to overturn the 2020 election.
In a letter to Mr. Gingrich, the Georgia Republican who held the speakership in the late 1990s, the committee said its investigators had obtained evidence that he was in contact with senior advisers to Mr. Trump about television advertisements that amplified false claims of fraud in the 2020 election and other aspects of the scheme to block the transfer of power, both before and after a mob attacked the Capitol.
“Some of the information we have obtained includes email messages that you exchanged with senior advisers to President Trump and others, including Jared Kushner and Jason Miller, in which you provided detailed input into television advertisements that repeated and relied upon false claims about fraud in the 2020 election,” Representative Bennie Thompson, Democrat of Mississippi and chairman of the committee, wrote in a letter to Mr. Gingrich.
“These advertising efforts were not designed to encourage voting for a particular candidate,” Mr. Thompson added. “Instead, these efforts attempted to cast doubt on the outcome of the election after voting had already taken place. They encouraged members of the public to contact their state officials and pressure them to challenge and overturn the results of the election.”
The letter to Mr. Gingrich asked that he preserve all records and communications he had with the White House, Mr. Trump, the Trump legal team and others involved in the events of Jan. 6. It requested that he sit for an interview during the week of Sept. 19.
Mr. Thompson said Mr. Gingrich pushed messages explicitly designed to incite anger among voters, even after Georgia election officials had faced intimidation and threats of violence. In particular, Mr. Gingrich advocated promoting the false claims that election workers in Atlanta had smuggled in fake votes in suitcases.
“The goal is to arouse the country’s anger through new verifiable information the American people have never seen before,” Mr. Gingrich wrote to Mr. Kushner, Mr. Miller and Larry Weitzner, a media consultant, on Dec. 8, 2020. “If we inform the American people in a way they find convincing and it arouses their anger, they will then bring pressure on legislators and governors.”
He also pushed for a coordinated plan to put forward pro-Trump electors in states won by Joseph R. Biden Jr.
On Nov. 12, 2020, Mr. Gingrich wrote to Mr. Trump’s chief of staff, Mark Meadows, and the White House counsel Pat A. Cipollone, asking: “Is someone in charge of coordinating all the electors?”
On the evening of Jan. 6, Mr. Gingrich continued to push efforts to overturn the election, emailing Mr. Meadows, at 10:42 p.m. after the Capitol had been cleared of rioters, asking if there were letters from state legislators about decertifying the results of the election.
“Surprisingly, the attack on Congress and the activities prescribed by the Constitution did not even pause your relentless pursuit,” Mr. Thompson wrote.
Mr. Gingrich did not immediately respond to a request for comment.
The letter to Mr. Gingrich comes as investigations of the attack on the Capitol have intensified.
Two of Mr. Trump’s top White House lawyers are set to testify on Friday before a federal grand jury investigating the riot, according to a person familiar with the matter. The scheduled appearances of Pat A. Cipollone, the former White House counsel, and Patrick F. Philbin, who was his deputy, which were reported earlier by ABC News, could give investigators more insights into the former president’s actions after his election defeat.
Mr. Cipollone and Mr. Philbin were witness to key moments in Mr. Trump’s push to overturn the 2020 election results, including discussions about sending false letters to state officials, meddling in the Justice Department and seizing voting machines. Mr. Cipollone was also in direct contact with the president as rioters stormed the Capitol on Jan. 6.
At least five top former White House officials have received subpoenas from a Washington-based grand jury investigating the events that led to the violence, including Eric Herschmann, a lawyer who worked in the White House; Greg Jacob, the top lawyer for former Vice President Mike Pence; and Marc Short, Mr. Pence’s chief of staff.
The select committee has used the August congressional recess to gather more evidence as it prepares to resume public hearings this month, following up on thousands of submissions to its tip line, dispatching investigators to Europe and digging deeper into discussions after the riot by members of Mr. Trump’s cabinet about removing him from office.
The panel is also digging deeper into a fund-raising effort that Mr. Trump undertook after losing, raising millions from supporters who believed his lie of a rigged election. Investigators are also scrutinizing the matter of Secret Service text messages from Jan. 5 and Jan. 6, 2021, that were deleted.
But the panel is being met with resistance.
Douglas V. Mastriano, the Republican nominee for governor of Pennsylvania who served as a point person in the state for the plan to keep Mr. Trump in power by using slates of fake electors, filed suit against the committee Thursday, arguing that the panel has no authority to force him to sit for a deposition without a ranking Republican member appointed by the Republican Party.
Last month, Mr. Mastriano abruptly ended his interview with the panel after he objected to the committee’s rules about video recording.
For his part, Mr. Trump, who wants to make another White House run, said on Thursday on a Pennsylvania radio show that he had met with and planned to give financial support to some of the more than 850 people charged in connection with the riot.
“I will be looking very, very strongly at pardons — full pardons,” he said during an interview on Wendy Bell Radio.
“It’s a disgrace what they’ve done to them,” Mr. Trump said of the defendants.
Maggie Haberman and Alan Feuer contributed reporting.