CLEVELAND—The plagiarism in Melania Trump’s speech last night at the convention here is an issue because a) it happened; b) the Trump people are insisting on denying that it happened, which makes all of them from Paul Manafort to Chris Christie literally look and sound like they’re in need of psychiatric intervention; c) because of their psychosis, this is going to be talked about for far longer than it would have been had someone just said the non-native-English-speaking Melania was relying on help from a speechwriter who did a bad thing and is being fired, and; d) because it’s funny.

But far more important than all these is the very real possibility that the party’s nominee for president is now sitting around in a hotel suite brooding over the injustice being done to his wife, and what this is going to do to his cast of mind during the most important week of his life.

Is he blaming the media? Is he blaming Manafort, the campaign manager whose particular expertise is in running conventions? Is he thinking of firing someone? Is Mrs. Trump angry? Is she yelling at him?

He needs to make the public appearance of his lifetime in two days, and he has a particular problem with finding and maintaining focus. The last thing he needed was to be thrown off by this unexpected screw-up.

The danger for Trump is his poor impulse control. If the offense done to his wife gets in his head and stays there, he’s going to find it very difficult not to go off on a personal tangent about it during his acceptance speech on Thursday night. If so, he’ll have worked himself up into a quiet rage about it and will not be able to restrain himself from the podium. He’ll do what he does at his rallies, where he spins himself into a lather and looks, well, unhinged. Those who love him won’t mind. Many other people will think he’s weird at best and crazy at worst.

Which last has the advantage of being the truth, but it won’t help him get to the presidency from here.