As to the president, one thought. He will never lead effectively at moments like this because he can’t. It’s not within his emotional range or in his intellectual toolbox. The targets of the would-be bombs have been his antagonists. He’s not believable when he issues pained vows of unity. Everyone assumes his staff told him to do it and in a burst of amiability he did. When he’s obnoxious, people believe he’s speaking his mind.

Mr. Trump has ushered in a new presidential era of verbal roughness. At his rallies he sees himself as being provocative and humorous and teasing. His crowds know he is entertaining them and they have fun back, re-enacting their old 2016 fervor with “Lock her up!” and “Build the wall!” They don’t emerge whipped into a rage; they leave in a good mood, though tired from standing so long because he speaks so long.

The president knows half the country is watching, and dislikes and disdains what it sees. What he doesn’t seem to know is that the unstable are watching, too. They get revved up, ginned up, pro and con. There is danger in this.

Mr. Trump seems to think only about his audience and his foes. He doesn’t seem to proceed with a broad knowledge that there are the unstable among us, and part of your job as president is not to push them over the edge. It can get ugly when you do.