The federal judge presiding over the classified documents case against former President Donald Trump is hearing arguments Friday on a long-shot defense effort to get the indictment thrown out based on the claim that the prosecutor who brought the charges was illegally appointed.

The arguments over the legality of special counsel Jack Smith’s appointment kick off a three-day hearing that is set to continue next week and bring further delays to a criminal case that had been scheduled for trial last month but has been snarled by a pileup of unresolved legal disputes. The motion questioning Smith’s selection and funding by the Justice Department is one of multiple challenges to the indictment the defense has raised, so far unsuccessfully, in the year since the charges were brought.

Even as Smith’s team looks to press forward on a prosecution seen by many legal experts as the most straightforward and clear-cut of the four prosecutions against Trump, Friday’s arguments before U.S. District Judge Aileen Cannon won’t involve discussion of the allegations against the former president. They’ll center instead on decades-old regulations governing the appointment of Justice Department special counsels like Smith, reflecting the judge’s continued willingness to entertain defense arguments that prosecutors say are meritless, contributing to the indefinite cancelation of a trial date.