A federal judge on Thursday narrowed the scope of questions that Republican Senator Lindsey Graham must answer from a special grand jury investigating Donald Trump's effort to overturn the 2020 election results in Georgia, but she again rejected Graham's bid to avoid testifying altogether.

In a 23-page ruling, U.S. District Judge Leigh Martin May in Atlanta said the U.S. Constitution protects Graham from having to discuss any "investigatory fact-finding" he was engaged in during two phone calls he made to Georgia election officials following the 2020 election. Democrat Joe Biden's victory in the state helped propel him to the White House.

However, she ruled that the grand jury is free to ask Graham about other subjects, including "any alleged efforts" to encourage state election officials to "throw out ballots" as well as any coordination that may have existed between Graham and the Trump campaign.

Graham's office did not immediately comment on the ruling or indicate whether he plans to appeal.

Fulton County District Attorney Fani Willis, a Democrat, opened a criminal probe after a January 2021 recorded phone call in which Trump urged Georgia Secretary of State Brad Raffensperger, the state's top election official, to "find" enough votes to alter the outcome.

Her office convened the grand jury in part to issue subpoenas for witnesses, including key Trump advisers such as Rudy Giuliani.

The Georgia probe is one of several involving Trump, including a Justice Department investigation into whether the former president violated the law by transporting classified government documents to his Florida estate.

May had previously denied Graham's attempt to quash the Fulton County subpoena, but the 11th U.S. Circuit Court of Appeals ordered her to consider whether to partially grant his request based on constitutional protections for sitting members of Congress.