A source told The News that de Blasio tried to get Banks to change his mind. Insiders have said Banks was being groomed as a possible replacement for Bratton whenever he steps down. Ed Mullins, head of the Sergeants Benevolent Association, said he was sorry to see Banks leave — but not as sorry as the mayor. "Politically, it's a nightmare for the mayor," he said. Public Advocate Letitia James, in an unlikely pairing, echoed the union head. "The fact that 10 months into this administration the top uniformed police officer believed that he had to resign is deeply troubling," she said.