The probe by the Fulton County, Georgia, district attorney into former President Donald Trump’s election fraud allegations has entered a more combative stage, as former Trump lawyer and New York City Mayor Rudy Giuliani is expected to testify as soon as Wednesday. 

In an order handed down Monday, U.S. District Judge Leigh Martin May ruled that U.S. Sen. Lindsey Graham also could not dodge a subpoena and will testify before a special grand jury on Aug. 23 related to Fulton County District Attorney Fani Willis’ more than 18-months-long investigation into Trump. 

Last month, Willis filed petitions seeking to compel testimony from seven Trump advisers and associates. 

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. 

REP. BISHOP SAYS FBI TRUMP RAID SHOWS DANGEROUS ‘SECURITY STATE,' AMERICANS FEEL GOV'T ‘OUT OF THEIR CONTROL’

Georgia prosecutor Fani Willis

Fulton County District Attorney Fani Willis during an interview at her office, Feb. 24, 2021, in Atlanta.  ((AP Photo/John Bazemore, File))

Willis’ office successfully blocked Giuliani’s attempt to delay his testimony during the same week the FBI raided Trump residence at Mar-a-Lago in Florida. Two days after the raid, Trump, meanwhile, pleaded the Fifth in a deposition for New York Attorney General Letitia James

The Atlanta Journal-Constitution reported that Willis has been ramping up her investigation in recent weeks ahead of the November midterm elections anticipating that an announcement by Trump that he would run for a second term in 2024 could put a wrench in her probe. 

A 23-person special purpose grand jury has subpoenaed dozens of witnesses from as far as New Mexico and New York to testify as Willis examines whether Trump or his associates broke any Georgia state law while attempting to have the 2020 presidential election result overturned.  

Lindsey Graham at SC GOP dinner

Sen. Lindsey Graham, R-S.C., addresses a South Carolina GOP dinner July 29, 2022, in Columbia, S.C.  (AP Photo/Meg Kinnard, File)

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. 

Giuliani in NYC for son's gubernatorial campaign

Rudy Giuliani appears in support of his son, New York Republican gubernatorial primary candidate Andrew Giuliani, at an election night watch party in Manhattan on June 28, 2022, in New York City. Andrew Giuliani lost to Rep. Lee Zeldin, R-N.Y., who will take on Democratic Gov. Kathy Hochul this fall.  ((Photo by Spencer Platt/Getty Images))

The judge also rejected Graham’s argument that the principle of "sovereign immunity" protects a senator from being summoned by a state prosecutor. Last month, May rejected a similar attempt by U.S. Rep. Jody Hice, R-Ga., to avoid testifying before the special grand jury. 

CLICK HERE TO GET THE FOX NEWS APP

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

The Associated Press contributed to this report.