American political rhetoric has crossed the line into incitement before: Think the right-wing paranoia-stoking before the Oklahoma City bombing, or the left-wing online communities that produced the shooter of a GOP Congressman at a softball practice last year.

In that sense, Cesar Sayoc Jr., the man arrested Friday for sending crude pipe bombs to media and to political figures viewed as critical of President Trump, looks like a sadly familiar figure. Middle-aged? Check. Male? Check. Politically disaffected? Check. He would appear to be cut from the same cloth as earlier crackpots.

What’s critically different is the source of incitement in Cesar Sayoc’s America. The vitriol isn’t originating with extremist talk radio voices or obscure Internet forums. It’s coming from the president of the United States himself. In his tweets and public statements, he is coarsening political dialogue and plunging the nation to dangerous new lows. It took quite the straight face for the president to say, after the arrest on Friday, that “we must never allow political violence to take root in America.’’ He added, “I’m committed to doing everything in my power as president to stop it.’’

That’s not true. Just this week, Trump endorsed political violence when he praised a Congressman who’d body-slammed a reporter. And his willingness to wink at extremist groups at last year’s Charlottesville march can’t be forgotten. He’s become a bully in chief, belittling political opponents using harsh language with violent undertones. Trump’s words are having terrible consequences — at home and abroad. His endorsement of violence and his crude attacks on the press give license to kill or silence critics.

It needs to stop. John O. Brennan, the former CIA director, may have put it best, in a tweet directed at Trump on Thursday:

“Stop blaming others. Look in the mirror. Your inflammatory rhetoric, insults, lies, & encouragement of physical violence are disgraceful. Clean up your act . . . try to act Presidential. The American people deserve much better. BTW, your critics will not be intimidated into silence.’’

There’s no straight line between the president’s tweets and the accused bomber’s alleged attacks. There never is. But when the president and his supporters openly talk about violence against their critics, they create an atmosphere that can only embolden people like Sayoc.