OF ALL the irresponsible things that President Trump has said — and there have been far too many — perhaps nothing threatens to do greater damage than his remarks encouraging police to use excessive force. That was demonstrated by the swift public condemnations of his comments from police officials, who understand better than anyone that public safety is not well served if police are seen to be above the law and distrusted.

“Please don’t be too nice” was Mr. Trump’s admonition, to a gathering of law enforcement officials, about arresting and transporting suspects. “When you guys,” he said Friday at an event on Long Island, “put somebody in the car and you’re protecting their head, you know, the way you put their hand over? Like, don’t hit their head, and they’ve just killed somebody — don’t hit their head. I said, you can take the hand away, okay?” As alarming as his comments were, even more jarring was the spectacle of officers in uniform cheering and applauding. Do they need a reminder of 25-year-old Freddie Gray and how he died from a spinal injury after transport in a Baltimore police van in 2015?

It was heartening, though, to see police officials from across the country distance themselves from — with many firmly denouncing — the president’s comments giving a seeming wink and nod to police brutality. New York’s Suffolk County Police Department, which had officers present at the Friday event, said it has strict rules and procedures that don’t tolerate the “roughing up of prisoners.” New Orleans Police Superintendent Michael Harrison said unreasonable or unnecessary use of force “erodes trust at a time when we need support from our local communities the most.” Montgomery County Police Chief J. Thomas Manger was, as he bluntly writes on this page, “appalled” to hear such comments from the president of the United States.

Unfortunately and to its discredit, the national union representing police rank and file attempted to give Mr. Trump a pass for his unacceptable remarks. “Off the cuff comments . . . are sometimes taken all too literally by the media and professional police critics,” said a statement from National Fraternal Order of Police President Chuck Canterbury. His cavalier attitude disserves his union’s members, most of whom conscientiously follow the law while performing their difficult and dangerous duty.

Given that the Justice Department under Attorney General Jeff Sessions has signaled its lack of interest in bringing needed reform to troubled police departments, in the name of law and order, it is hard not to be concerned by the president’s comments. And even if Mr. Trump really didn’t mean what he said — the all-too-convenient excuse used by his apologists — we agree with former D.C. and Philadelphia police chief Charles H. Ramsey (hardly a professional police critic) that “words matter.” Mr. Trump’s paean to gratuitous use of force sends the wrong message to police and to the communities they serve.