Mayor Eric Adams’s decision to appoint Thomas Donlon, a 71-year-old former F.B.I. investigator, as New York’s interim police commissioner seemed to bring a sense of stability to a department rocked by several federal inquiries. It didn’t last long.

On Sept. 21, a week after his appointment, Mr. Donlon acknowledged that he was also the subject of a federal probe. F.B.I. agents had come to his home with a warrant and demanded he return files he had taken more than 20 years ago when he left the agency. Almost immediately, reports began circulating that Mr. Donlon would go the way of other City Hall executives who had resigned amid the crisis.

His acting chief of staff, Terri Tobin, and other supervisors assigned to his office stepped aside about a month after they started their roles for reasons that remain unclear, according to two people with knowledge of the change.

On Nov. 3, the commissioner had a public spat during the New York City Marathon with his acting chief of staff, Tarik Sheppard. The men, according to two people briefed on the incident, argued so vociferously during a photo opportunity that they had to be separated. The incident forced Mr. Adams to answer questions about infighting.

Yet two months in, Mr. Donlon remains and has told friends and people at the department that he wants to stay.

“He has no intention of leaving,” said Mark Carroll, a friend and retired federal prosecutor who has known him for 44 years. “He likes the job, and he likes the work. He enjoys helping people and doing public service. That’s been his whole career.”