Mr. Meadows was also involved in trying to reverse Mr. Trump’s defeat in Georgia. He was in “constant contact” with Mr. Trump in the weeks after the 2020 election, according to court filings from Ms. Willis’s office. The filings note that Mr. Meadows, by his own public admission, attended a meeting at the White House on Dec. 21, 2020, with Mr. Trump, members of Congress and others to discuss allegations of voter fraud in the state.

The next day, Mr. Meadows made a surprise visit to Cobb County, Ga., accompanied by Secret Service agents, intending to view an audit that was in progress there. Local officials declined to let him do so because the audit was not open to the public.

Mr. Meadows also talked to Frances Watson, the chief investigator for Brad Raffensperger, the Georgia secretary of state, who was conducting an inquiry into ballot signatures in Cobb County. That call was made the day before Mr. Trump phoned Ms. Watson himself, telling her: “When the right answer comes out, you’ll be praised.”

Prosecutors say that the special grand jury has evidence that Mr. Meadows set up the phone call on Jan. 2, 2021 in which Mr. Trump can be heard telling Mr. Raffensperger he wanted to “find” the 11,780 votes that would allow him to win in Georgia.

In August, in a material witness certificate seeking Mr. Meadows’s testimony, Judge McBurney noted that Mr. Meadows “actively participated in and spoke” during the Jan. 2 call.

Mr. Meadows and Mr. Raffensperger are Republicans. Ms. Willis is a Democrat.

Dozens of witnesses have already testified before the special-purpose grand jury. When an out-of-state witness is subpoenaed, a court hearing is held where the witness lives, to determine whether the witness must comply. A number of Trump allies have used those hearings to try to fight their subpoenas.

Among those who lost their fights are the lawyers Jenna Ellis, from Colorado, and John Eastman, from New Mexico. When lawyers for Rudolph W. Giuliani, Mr. Trump’s former personal lawyer, argued that he was too ill to fly to Atlanta from his home in New York, a judge in Atlanta said that Mr. Giuliani could come “on a train, on a bus or Uber.”