Patrick Lynch, president of the Patrolman's Benevolent Association, arrives at a makeshift memorial, on Monday, Dec. 22, 2014, near the site where New York Police Department officers Rafael Ramos and Wenjian Liu were murdered in the Brooklyn borough of New York. (John Minchillo/AP)

THE COLDBLOODED killings of two New York City police officers Saturday was a terrible, vicious crime. It also has been the occasion for some wrong-headed commentary that needs correcting.

Ismaaiyl Brinsley, a disturbed New York native with a history of at least 20 arrests, assassinated Officers Rafael Ramos and Wenjian Liu as they sat in their patrol car in Brooklyn. Officer Ramos, 40, was a well-liked and devoted policeman who looked forward to taking his two boys to play basketball in the park whenever he could. Officer Liu, 32, had celebrated his wedding just three months ago. “I know that being a cop is dangerous but I must do it,” he told a friend, as the New York Times reported. “If I don’t do it and you don’t do it, then who is going to do it?”

The officers are being mourned and celebrated in New York and across the country, as they should be. But their deaths also have been improperly used in a political debate. Republican politicians, such as former New York mayor Rudolph W. Giuliani, and police union leaders in Baltimore and New York have blamed the killings on people protesting police tactics after civilians were killed by officers in Ferguson, Mo., Staten Island and elsewhere.

“We’ve had four months of propaganda, starting with the president, that everybody should hate the police,” Giuliani said on “Fox and Friends Weekend.” “I don’t care how you want to describe it: That’s what those protests are all about.” Patrick Lynch, a police union leader in New York, agreed: “There’s blood on many hands tonight,” he said late Saturday. “Those that incited violence on the street in the guise of protest, that tried to tear down what New York City police officers did every day.”

We don’t doubt that some police officers have felt aggrieved by the protests nor that a few protesters have gone too far in their vilification, not just of police methods but of police officers. It was heartbreaking to read the Facebook post of Officer Ramos’s son, Jaden, 13. “Everyone says they hate cops,” Jaden wrote, “but they are the people that they call for help.”

But those who have protested the killings of Eric Garner, Michael Brown and others bear no responsibility for the twisted mind and crimes of Mr. Brinsley, who committed suicide after killing the two officers. On the contrary: It is in the long-term interest of the police, as well as of the communities they serve, to shape reforms that might reduce the incidence of police violence while still valuing officers’ safety and fighting crime. As Eric Adams, Brooklyn borough president and a former police captain, told the Times, “Calling for reform is not a call for harm of police officers.”

Not so many years ago, everyone seemed to be celebrating the “broken-windows” method of policing, which held that refusing to tolerate small infractions such as graffiti would reduce the incidence of more serious crime, too. Now protesters are calling for less aggressive enforcement of misdemeanor offenses, which they say sweeps too many poor, minority men into the criminal justice system. Finding the right balance won’t be easy. It’s made more difficult by inflammatory, unsupported rhetoric like that of Mr. Giuliani.