The deaths of Michael Brown and Eric Garner at the hands of police last year have reignited the war liberals have waged against our cops. It’s “our cops” — not “the cops” — because no matter what our race, religion, economic circumstance, we all rely on the police for our families’ safety.

This is a political war that liberals have waged for decades in protests, newspapers and even in song. According to the Progressives Today website, protesters in Portland, Oregon, sang “Deck the halls with rows of dead cops,” on Dec. 28. The “brave protesters,” according to the report, did so while blocking streets in supposed demonstration against the death of Michael Brown.

These are the same sorts of people who have — at least three times — invited Wesley Cook to speak at college commencements. The latest, held at Goddard College in Vermont, was announced in September by interim college President Bob Kenny. He said, “Choosing [Cook] as their commencement speaker, to me, shows how this newest group of Goddard graduates expresses their freedom to engage and think radically and critically in a world that often sets up barriers to do just that.”

That announcement drew condemnation from Maureen Faulkner. Who is she to object? She is the widow of Philadelphia cop Daniel Faulkner, whom Cook — now known as Mumia Abu-Jamal — murdered in 1981. First condemned to death for the brutal killing, Abu-Jamal is serving a life sentence without parole. He delivered his address by video recorded in his jail cell to satisfy the Goddard students’ hunger for “thinking radically and critically.”

But for the success of this political war on police, people such as New York Mayor Bill de Blasio would probably not be in office, men such as Al Sharpton wouldn’t be prominent in a liberal parody of the civil rights movement (and as an adviser to President Obama) and newspapers such as The New York Times wouldn’t be waging the war on their editorial pages. And cop killers such as Mumia — as he is popularly known — wouldn’t be lionized.

People such as Mr. Obama, Mr. de Blasio and the editors who wrote The New York Times editorial grew up among the protesters. They exhibit the groupthink that depends on a narrative that police are racist oppressors of the black community. One retired police officer I know is disgusted by them. He has told me many times that these liberals need to understand how the supposedly oppressed minority relies on the cops to come when they call. He says they should ride along with a police patrol one night in a minority community to see just how the people depend on the police to protect them from the crime that truly oppresses too many black communities.

Mr. Obama and Mr. de Blasio have earned the distrust and resentment of the police. Mr. Obama, from the moment he came into office, took sides against the police even when he acknowledged that he didn’t know the facts. In 2009, he said a Cambridge, Massachusetts, police officer “acted stupidly” in arresting his pal, a Harvard professor, and then held his “beer summit” between the arresting officer and the professor. When Trayvon Martin was killed by George Zimmerman, who wasn’t a police officer, Mr. Obama said the youth could have been his son or even himself years ago. When a grand jury decided against an indictment of the police officer who shot Michael Brown, Mr. Obama stuck with the “police as oppressors” narrative. Whenever a president’s words could have led to lesser tensions between police and minority communities, Mr. Obama sowed discord.

Mr. de Blasio earned the distrust and resentment of New York’s Finest by word and deed. During his campaign, he reportedly stepped away from his New York Police Department protective detail, fearing they would eavesdrop on his political maneuvers. He campaigned against the “stop and frisk” policy that has been upheld by the courts (despite accusations of racial bias) and is responsible for reducing New York’s crime rates. When Garner’s death did not result in an indictment of the police officer involved, Mr. de Blasio spoke about how he and his wife have had to talk to their son “for years about the dangers that he may face.” Which dangers? From the police, of course. Mr. de Blasio said, “We’ve had to literally train him, as families have all over this city for decades, in how to take special care in any encounter he has with the police officers who are there to protect him.”

It’s no wonder that police blame Mr. de Blasio for stoking the fear and resentment of the police that they believe led to the assassinations of two police officers Dec. 20. The mayor earned, by conscious effort, the protests that led to officers turning their backs to him.

The shooting deaths of police officers rose more than 50 percent nationwide last year. It’s time for the president, the mayor and the media to calm this resentment and these fears. But they don’t.

The New York Times predictably chose to defend Mr. de Blasio and accuse the NYPD of “disgraceful” conduct in turning their backs on him and harboring a “snarling sense of victimhood.” The cops don’t understand that the snarling sense of victimhood is politically permitted only to liberals such as those who sing “Deck the halls with rows of dead cops.”

The NYPD officers aren’t snarling. They’re out there every day and every night protecting the people who throw curses at them. For the New York cops, and all good cops nationwide, we should give thanks.

• Jed Babbin is a former deputy undersecretary of defense in the George H.W. Bush administration and co-author of “The Sunni Vanguard” (London Center for Public Policy, 2014).