It is the sequence that every mayor dreads: the ominous report, the scramble to the hospital and the confirmation that, yes, an attack against the police has proved fatal.
But for Mayor Bill de Blasio, the tragedy on Saturday — when two police officers were shot and killed in an ambush in Brooklyn, according to the authorities — arrived at a particularly trying moment, amid an already fractious relationship with the police.
Police union leaders and officers could be seen turning their backs to the mayor and the police commissioner, William J. Bratton, as they walked past, in a video taken at the hospital where the two held a news conference on Saturday.
A written message from Edward Mullins, president of the Sergeants Benevolent Association, addressed the mayor directly. “Mayor de Blasio,” it read in part, “the blood of these two officers is clearly on your hands.”