Protesters and Donald Trump supporters clash on March 11 after a Trump campaign event at the University of Illinois at Chicago was postponed. (Jabin Botsford/The Washington Post)

DONALD TRUMP boasts about his ability to deliver on his words. When he talks about wanting to “punch . . . in the face” or “knock the crap out” of people protesting him, he knows exactly what he is doing — and what is likely to result. So it’s really rich to see him attempt to distance himself from the violence and ugliness that have become staples of his campaign appearances.

There has long been an undercurrent of menace at the massive, revival-like rallies that Mr. Trump holds throughout the country, but a series of troubling events and Mr. Trump’s attempt to capi­tal­ize on them escalated the problem last week. During a rally in North Carolina, a young black protester being escorted from the event was punched in the face by a Trump supporter who, before being arrested, bragged about “knocking the hell out of that big mouth . . . The next time we see him we might have to kill him.” At an event in Kentucky, a black woman holding an anti-Trump sign was violently shoved by a group of white men and called obscene names. An Arab American reporter covering a rally in Virginia was derided as a terrorist, and a Breitbart reporter was manhandled by Trump’s campaign manager.

Mr. Trump was pressed on the issue at Thursday’s Republican debate by CNN’s Jake Tapper, who asked him if he has done anything to create a tone that encourages this kind of violence. “I hope not. I truly hope not,” he said. It was a denial undermined when his own words were thrown back at him. “I’d like to punch him in the face,” he said on Feb. 23. “In the good ol’ days, they’d have ripped him out of that seat so fast,” he said on Feb. 27. And, from Feb. 1: “Knock the crap out of him, would you? Seriously. Okay, just knock the hell. I promise you I will pay for the legal fees, I promise, I promise.”

If there were any doubt about Mr. Trump’s culpability as an instigator, it was erased Friday during a press conference announcing his endorsement by Ben Carson. Mr. Trump doubled down on his complaints about protesters — “bad dudes,” he called them Thursday night — and defended his supporters’ right to “hit back.” Litttle wonder, then, that there were clashes later that day between Trump supporters and protesters at an event in Chicago, prompting Mr. Trump to cancel the event with too-little, too-late protestations about wanting to avoid violence.

What’s particularly contemptible is Mr. Trump’s attempt to rationalize the thuggery as an understandable outgrowth of his followers’ angst. “When they see what’s going on in this country, they have anger that’s unbelievable,” he said during the CNN debate.

Many presidential candidates, this year and in campaigns past, have managed to deal with disruptions to their events without resorting to hooliganism. Mr. Trump’s Republican rivals were right to call him out for creating an environment that has caused such frightening hostility. There can be only one answer to incitement to violence from anyone who seeks to be president of the United States, and that is to unequivocally condemn it. Mr. Trump’s tactics must not be accepted into American political life.