By David Morgan

WASHINGTON (Reuters) -Republicans who control the U.S. House of Representatives on Thursday launched an investigation of Fulton County, Georgia, District Attorney Fani Willis, as former President Donald Trump prepared to report to jail on criminal charges she brought involving his efforts to overturn his 2020 election loss.

House Judiciary Committee Chairman Jim Jordan, one of Trump's staunchest allies in Congress, sent a letter to Willis asking whether she coordinated her state investigation of Trump with the U.S. Justice Department, including Special Counsel Jack Smith, or used federal tax money in carrying out the probe.

"The federal government has a substantial interest in the welfare of former presidents," Jordan told Willis in the five-page letter.

"And because this former president is a current candidate for that office, the indictment implicates another core federal interest: a presidential election," Jordan said.

Jordan and two other House Republican chairmen are pursing a similar probe of Manhattan District Attorney Alvin Bragg, who brought criminal charges against Trump involving hush money paid to a porn star ahead of the 2016 presidential election. In response, Bragg sued Jordan to stop what the district attorney called a "campaign of intimidation."

Trump has faced criminal charges in four cases this year, two brought by Smith. Trump, the first former U.S. president ever to face criminal charges, is the front-runner in the race for the Republican nomination to face President Joe Biden, a Democrat, in the 2024 U.S. election.

The House investigation of Willis was disclosed three days after Trump accused her on his social media platform of "continuing to campaign, and raise money on, this WITCH HUNT. This is in strict coordination with Crooked Joe Biden's DOJ. It is all about ELECTION INTERFERENCE!"

The House Judiciary Committee released Jordan's letter as Trump prepared on Thursday to be fingerprinted and photographed at an Atlanta jail on 13 felony counts including racketeering, which is typically used to target organized crime. Trump in the case brought by Willis was accused of unlawfully pressuring Georgia state officials to reverse his 2020 election loss to Biden in the state.

House Republicans have sought to defend Trump against the charges in four cases by alleging that the U.S. justice system has been "weaponized" against him by Biden.

Trump, 77, faces 91 separate criminal counts overall in the court cases. He has denied any wrongdoing.

(Reporting by David Morgan; Editing by Will Dunham and John Stonestreet)