Last weekend was not only the warmest on record so far this year in NYC, but the most violent. Three people were killed and 23 wounded in 21 shootings between Friday and Sunday.

If, as NYPD Commissioner Bill Bratton has said, "Jack Frost is the best friend of the police officer," warm weather is one of the cop's biggest enemies. And as we look to what could be a hot summer, some fear last weekend may only be a precursor.

Unfortunately, nice weather isn't the only factor that may exacerbate crime. The spate of shootings comes as:

Mayor Bill de Blasio moves to reduce the number of inmates at Rikers Island. The administration has said pretrial inmates whose cases have been pending for more than a year will have court dates in the next 45 days. The goal of the policy, designed with Chief Judge Jonathan Lippman, is laudable, but it may lead to a flood of inmates released from Rikers.

The City Council seeks to decriminalize low-level offenses, including open containers and public urination. The plan, part of a change to broken-windows policing, was met with lukewarm support from Bratton, who has argued that tackling quality-of-life offenses helps deter more serious crimes.

De Blasio's administration pushed other changes, such as overhauling stop-and-frisk and police not arresting anyone caught with less than 25 grams of pot. Four months later, Bratton said that while crime in the city overall is down, homicides and shootings are up.

The late Republican strategist Lee Atwater was right that "perception is reality." When it comes to stop-and-frisk, the perception among many is that while it may have been unfairly executed, it also helped keep guns off the street. That doesn't mean it should be resurrected, but now the administration needs to find a way to get guns off the streets.

And, of course, this is de Blasio's main challenge. He was elected on a promise to change policing. Observers noted accurately then that he would have the support to make the changes as long as the public felt the city is safe. But that support could wane if the public perceives NYC is less safe than it was under his predecessor.

That is why what happened last weekend is so potentially politically debilitating for de Blasio.

Jeanne Zaino is professor of political science at Iona College and campaign management at NYU.