Prosecutors investigating former President Donald Trump's influence on the 2020 election in Georgia can compel South Carolina Republican Sen. Lindsey Graham to testify, a federal court ruled Thursday. 

Graham's claim of immunity to the investigation's questioning was rejected by the U.S. Court of Appeals for the 11th Circuit in Atlanta. 

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Republican South Carolina Sen. Lindsey Graham

Sen. Lindsey Graham (R-SC) speaks on southern border security and illegal immigration, during a news conference at the U.S. Capitol on July 30, 2021 in Washington, DC. (Kevin Dietsch/Getty Images)

The three-judge panel ruled that Graham cannot be questioned on his professional communications related to the legislature, but his personal conversations with Trump and other Georgia officials are fair game.

Fulton County District Attorney Fani Willis filed petitions with the judge overseeing the special grand jury as part of her investigation into what she alleges was "a multi-state, coordinated plan by the Trump Campaign to influence the results of the November 2020 election in Georgia and elsewhere." 

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Trump speaks at Nevada rally

FILE - Former President Donald Trump pauses while speaking at a rally at the Minden Tahoe Airport in Minden, Nevada, on Oct. 8, 2022. (AP Photo/José Luis Villegas, Pool, File)

Willis, who took this unusual step of requesting a special grand jury earlier this year, has confirmed that she and her team are looking into a January 2021 phone call in which Trump pushed Georgia Secretary of State Brad Raffensperger to "find" the votes needed for him to win the state. 

She has said the team is also looking at a November 2020 phone call between Graham and Raffensperger, the abrupt resignation of the U.S. attorney in Atlanta on Jan. 4, 2021, and comments made during December 2020 Georgia legislative committee hearings on the election. Raffensperger and other state officials have already testified before the special grand jury.

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Sen. Lindsey Graham of South Carolina

Sen. Lindsey Graham, R-S.C., the ranking member of the Senate Budget Committee, waits to speak to reporters following bi-partisan passage of the Ending Forced Arbitration of Sexual Assault and Sexual Harassment Act, at the Capitol in Washington, Feb. 10, 2022.  (AP Photo/J. Scott Applewhite, File)

The investigation is separate from that being conducted by a congressional committee that has been examining the events surrounding the riot at the U.S. Capitol on Jan. 6, 2021, as Congress was certifying Biden’s victory, as well as the Department of Justice's own sprawling probe.