In his office on the 14th floor of Police Headquarters, William J. Bratton displays copies of his memoir, “Turnaround,” his account of taming New York’s crime-filled streets and subways in the 1990s. On a mostly empty wall hangs a framed Time magazine cover from 1996, declaring over a steely photo of Mr. Bratton: “Finally, We’re Winning the War Against Crime. Here’s Why.”

The main “crises” he describes now, six months into his second tour as New York City police commissioner, are less likely to bring declarations of victory: frayed relations in minority communities; a department facing increased oversight; the ever-present threat of terrorism.

He is acutely aware of predictions that crime would rise in a post-stop-and-frisk New York run by a liberal mayor, Bill de Blasio, and Mr. Bratton accepts that, in many ways, his mandate is to bolster public confidence that the city will remain safe.

“A lot of this,” Mr. Bratton said, is about “effectively trying to just calm everybody down: ‘Hey, it’s going to be fine. The city is not going to fall apart. The four horsemen of the apocalypse are not riding into town to rape and plunder.’ ”