WASHINGTON — The House committee investigating the Jan. 6 riot at the U.S. Capitol has issued a subpoena to a former Justice Department lawyer who positioned himself as an ally of Donald Trump and aided the Republican president’s efforts to challenge the results of the 2020 election.

The subpoena to Jeffrey Clark, revealed Wednesday, came amid signs of a rapidly escalating congressional inquiry. At least three of the people who were involved in organizing and running the rally that preceded the violent riot are handing over documents in response to subpoenas from the committee.

The demands for documents and testimony from Clark reflect the committee’s efforts to probe not only the deadly insurrection but also the tumult that roiled the Justice Department in the weeks leading up to it as Trump and his allies leaned on government lawyers to advance his baseless claims that the election results were fraudulent.

Clark, an assistant attorney general in the Trump administration, has emerged as a pivotal character in that saga. A Senate committee report issued last week shows how he championed Trump’s efforts to undo the election results and clashed as a result with Justice Department superiors who resisted the pressure.