Jan. 6 Panel Subpoenas Jeffrey Clark, Former Justice Dept. Official

The House committee investigating the Jan. 6 Capitol riot issued a subpoena on Wednesday to Jeffrey Clark, a former Justice Department official under President Donald J. Trump who was involved in Mr. Trump’s frenzied efforts to overturn the 2020 presidential election.

The subpoena seeks testimony and records from Mr. Clark, a little-known official who repeatedly pushed his colleagues at the Justice Department to help Mr. Trump undo his loss. The panel’s focus on him indicates that it is deepening its scrutiny of the root causes of the attack, which disrupted a congressional session called to count the electoral votes formalizing President Biden’s victory.

“The select committee needs to understand all the details about efforts inside the previous administration to delay the certification of the 2020 election and amplify misinformation about the election results,” Representative Bennie Thompson, Democrat of Mississippi and the committee chairman, said in a statement. “We need to understand Mr. Clark’s role in these efforts at the Justice Department and learn who was involved across the administration.”

The subpoena was the 19th issued in the House inquiry, and it came as the panel braced for a potential legal battle with at least one prospective witness, Stephen K. Bannon, a former adviser to Mr. Trump who has refused to cooperate. The leaders of the committee threatened last week to seek criminal charges against Mr. Bannon in response.

Robert J. Costello, a lawyer for Mr. Bannon, did not back down in a letter to the committee on Wednesday, reiterating that his client would not produce documents or testimony “until such time as you reach an agreement with President Trump” on claims of executive privilege “or receive a court ruling.”