Attorneys for Graham, a Republican, had argued that his position as a U.S. senator provided him immunity from having to appear before the investigative panel and asked the judge to quash his subpoena. But U.S. District Judge Leigh Martin May wrote in an order Monday that immunities related to his role as a senator do not protect him from having to testify. Graham's subpoena instructs him to appear before the special grand jury on August 23, but he is expected to appeal the judge's ruling.

Fulton County District Attorney Fani Willis opened the investigation last year, and a special grand jury with subpoena power was seated in May at her request. Last month she filed petitions seeking to compel testimony from seven Trump advisers and associates.

Prosecutors have indicated they want to ask Graham about phone calls they say he made to Georgia Secretary of State Brad Raffensperger and his staff in the weeks following Trump's election loss to Democrat Joe Biden.

Graham had argued that a provision of the Constitution provides absolute protection against a senator being questioned about legislative acts. But the judge found there are "considerable areas of potential grand jury inquiry" that fall outside that provision's scope. The judge also rejected Graham's argument that the principle of "sovereign immunity" protects a senator from being summoned by a state prosecutor.

Graham also argued that Willis, a Democrat, had not demonstrated extraordinary circumstances necessary to compel testimony from a high-ranking official. But the judge disagreed, finding that Willis has shown "extraordinary circumstances and a special need" for Graham's testimony on issues related to alleged attempt to influence or disrupt the election in Georgia.

May, the judge, last month rejected a similar attempt by U.S. Representative Jody Hice, a Republican, to avoid testifying before the special grand jury. Former New York mayor and Trump attorney Rudy Giuliani had argued he couldn't travel to Atlanta to testify because of health issues, but Fulton County Superior Court Judge Robert McBurney, who's overseeing the special grand jury, instructed him to appear on Wednesday.

A Graham spokesperson, Kevin Bishop, said Monday the senator had no comment but referred to what Graham said when asked about the probe last week. During a news conference in Columbia, South Carolina, Graham said, "We will take this as far as we need to take it" when asked about his efforts to fight his subpoena.

"I was chairman of the Senate Judiciary Committee and had to vote on certifying an election," Graham told reporters. "This is ridiculous. This weaponization of the law needs to stop. So I will use the courts. We will go as far as we need to go and do whatever needs to be done to make sure that people like me can do their jobs without fear of some county prosecutor coming after you."

In calls made shortly after the 2020 general election, Graham "questioned Secretary Raffensperger and his staff about reexamining certain absentee ballots cast in Georgia in order to explore the possibility of a more favorable outcome for former President Donald Trump," Willis wrote in a petition.

Graham also "made reference to allegations of widespread voter fraud in the November 2020 election in Georgia, consistent with public statements made by known affiliates of the Trump Campaign," she wrote.

Republican and Democratic state election officials across the country, courts and even Trump's attorney general found there was no evidence of any voter fraud sufficient to affect the outcome of his 2020 presidential election loss.