Alabama election law requires candidates to withdraw at least 76 days before an election in order to be replaced on the ballot, a deadline Mr. Moore has already missed.

State law gives the governor broad authority to set the date of special elections, and Ms. Ivey, who is a Republican, already rescheduled the Senate election once, after inheriting the governor’s office in April when her predecessor, Robert Bentley, resigned in a sex and corruption scandal. Ms. Ivey’s advisers have not ruled out exercising that power again, according to Republicans in touch with her camp, but she has signaled that she would like reassurances of support from the White House before taking such an aggressive step.