(The Hill) — Republican Sen. Lindsey Graham of South Carolina is renewing his efforts to block a special grand jury subpoena for his testimony as part of an investigation into former President Donald Trump’s efforts to pressure Georgia officials to overturn the 2020 election results.

Court filings submitted late Friday show that Graham has tapped Trump’s former White House Counsel Don McGahn as part of his legal team in a federal lawsuit to quash the subpoena from Fulton County District Attorney Fani Willis, a Democrat.

Graham asked the federal district court in Georgia to hear the case on an expedited basis citing the subpoena’s Aug. 23 deadline. His lawyers argued that the Constitution expressly shields federal lawmakers from being compelled to testify in such state court proceedings.

“A federal court would be ordering a U.S. Senator from a coequal branch of government to appear before a grand jury,” the filing reads. “And enforcement would pose an even larger problem: It would create a precedent that would allow other county officials in locales across the nation to impose similar burdens on federal officials, of whatever party, to the detriment of our federal government and the federalism that protects it from state and local interference. And to what end? There is no need for Senator Graham’s testimony, far less ‘extraordinary circumstances’ compelling it.”

Willis has demanded Graham’s testimony regarding phone calls he made to a pair of state officials after the 2020 election.

Graham had previously filed a lawsuit in South Carolina federal court but agreed to dismiss the case and re-file it in the U.S. District Court for the Northern District of Georgia.

McGahn, his new attorney, served as White House counsel for Trump from the beginning of the administration in 2017 to fall 2018.

Graham’s lawyers argued the senator’s testimony would not be useful for Willis’s investigation, saying he took no part in any effort to overturn Georgia’s 2020 election results.

In their filing, his legal team wrote that Graham “was specifically exercising his oversight responsibilities as Chair of the Senate Judiciary Committee, including related to voting integrity and election-law issues.”