In a setback for Fani T. Willis, the Fulton County district attorney, a judge on Wednesday allowed defense lawyers in the Georgia criminal case against former President Donald J. Trump and his allies to try to appeal his ruling allowing Ms. Willis to stay on the case.

Defense lawyers needed permission from the judge, Scott McAfee of Fulton County Superior Court, to pursue an appeal, and he granted it in a two-paragraph order. Whether it slows down the election interference case against Mr. Trump and his 14 co-defendants remains unclear.

The Georgia Court of Appeals must still decide if it will weigh in on whether Ms. Willis has an untenable conflict of interest stemming from a romantic relationship she had with a lawyer she hired to run the Trump case, and on other related matters.

Judge McAfee wrote in his brief order that he “intends to continue addressing the many other unrelated pending pretrial motions” while the higher court decides what to do.

If the appeals court declines to take up the question, the matter will be resolved quickly. If it decides an appeal is warranted, the matter could take months to clear up.

In a statement, Jeff DiSantis, a spokesman for Ms. Willis’s office, said that prosecutors would continue to work on the case.