Fulton County District Attorney Fani Willis in a court filing said that claims that have threatened to upend her office's historic prosecution had "no merit," the Atlanta Journal-Constitution reported.

Trump and two co-defendants are seeking to disqualify Willis and dismiss the charges, alleging Willis benefited financially from an "improper, clandestine personal relationship" with Nathan Wade, a lawyer she hired to help lead the investigation.

The case is one of four criminal prosecutions Trump faces as he closes in on the Republican nomination to challenge Democratic President Joe Biden in November's elections. Trump has launched multiple challenges to these cases that could delay the start of any trial by weeks or months.

Citing unnamed sources and previously sealed court records, Trump co-defendant Michael Roman alleged in a court filing that Wade paid for vacations with Willis while he was being compensated by her office for work on the probe.

Trump and his co-defendants accused Willis of a conflict of interest and suggested her relationship with Wade may run afoul of state ethics rules and U.S. law.

Records released as part of Wade's divorce case show he paid for airline flights with Willis on at least two occasions during the investigation.

Trump's legal team endorsed Roman's allegations and said Willis "inappropriately injected race into the case" during a speech responding to Roman's allegations.

Willis said during the speech that she hired three special counsels for the election interference investigation and noted that only Wade, who like her is Black, has come under scrutiny.

In Georgia, Trump and 14 of his political allies are facing racketeering and other charges in a sweeping indictment accusing them of conspiring to reverse his narrow 2020 defeat in the state. Four defendants originally charged in the case have pleaded guilty after striking deals with prosecutors.

Fulton County Superior Court Judge Scott McAfee, who is overseeing the case, has scheduled a Feb. 15 hearing focused on the allegations.

(Reporting by Andrew Goudsward; Editing by Scott Malone and Daniel Wallis)