As NYPD commissioner under Mayor Rudy Giuliani two decades ago, Bill Bratton came in like gangbusters. Trying to stem a high homicide rate -- nearly 2,000 killings a year under Mayor David Dinkins -- Giuliani and Bratton fought crime 24/7.

At Police Plaza, Bratton brought in his own team, installed CompStat and insisted on accountability. After two years, homicides had dropped below 1,000 a year. Bratton had reached national stature, and he graced the cover of Time.

As he now completes his second year since returning as commissioner, accomplishments under Mayor Bill de Blasio have been more modest -- but in a much different city.

We don't know the terms of engagement between the two, but Bratton lobbied hard for the job and the mayor initially seemed to have set parameters. Although Giuliani let Bratton select his top staff, Bratton's first deputy and chief of department were selected by de Blasio. It took Bratton a year to rid himself of both.

For the first time in 20 years, the mayor's priority is not reducing crime. It is reining in the police and easing tensions between the NYPD and minority communities. Bratton accommodated himself to the idea. With crime at its lowest levels in NYC since the 1950s, Bratton called this "the peace dividend."

His most visible effort: reducing stop-and-frisk numbers. Commissioner Ray Kelly begun reducing them in 2012-13 after political fallout and court rulings. Bratton continued the reduction.

But many in the NYPD felt the mayor had inadvertently created a climate that encouraged a deranged Baltimore man to assassinate then-Officers Rafael Ramos and Wenjian Liu. Some officers turned their backs on de Blasio at the funerals for the two cops.

This has placed Bratton in an unexpected role -- as a buffer between the mayor and the police. But in July Bratton issued his declaration of independence, saying he wouldn't stick around much past the 2017 election. More recently, he blamed the deaths of Liu and Ramos on the protesters who demonstrated against department policy.

Twenty years ago, two months after Time's cover story, Giuliani fired Bratton with no credible public explanation.

Politically, de Blasio doesn't appear to have that option. For better or worse, he's stuck with Bratton.