Jan. 6 Panel Subpoenas Retired Colonel Who Shared Plan to Overturn Election

“Colonel in the military, great war record,” Mr. Giuliani later said of Mr. Waldron in a deposition he gave in a defamation lawsuit brought by a Dominion employee. “I’ve had substantial dealings with him and he’s very, very thorough and very experienced in this kind of work.”

Mr. Giuliani said his legal team put up a “big whiteboard” that laid out its strategies while he and fellow lawyers, including Ms. Powell and Jenna Ellis, ran operations as “really active supervisors.”

Mr. Giuliani said another lawyer, Boris Epshteyn, was focusing on fraud allegations in Nevada and Arizona, while Mr. Waldron was investigating conspiracies related to Dominion voting machines.

“If I were to think of Dominion, I would think of Sidney carrying the ball on that, with everybody else helping, and Phil was the investigator,” Mr. Giuliani said.

Mr. Waldron also participated in meetings at the Willard Hotel in Washington, D.C., in early January to plan ways to challenge the election results, according to the committee.

In the wake of the election, Mr. Waldron was working closely with a Texas-based company called Allied Security Operations Group, whose co-founder, Russell J. Ramsland Jr., was also helping Ms. Powell with her lawsuits by sending her affidavits claiming that Dominion’s voting machines could be easily hacked by foreign powers. As early as August 2020, even before a single vote was cast, according to court papers filed by Dominion on Tuesday, Mr. Ramsland had been hired by Patrick Byrne, the former chief executive of Overstock.com, to “reverse engineer” the evidence needed to “mislead people into believing” that Dominion helped steal the 2020 election.

But the legal campaign against Dominion was only one part of what amounted to a full-court press against the validity of the vote results. Mr. Ramsland also began to appear on right-wing media outlets like Fox News and Newsmax to promote conspiracy theories about the election. He claimed, for example, that computer servers based in Germany had been used to flip votes in the United States. Mr. Trump amplified that allegation on Twitter.