His campaign would remain competitive in the polling, I believe, but it’s a very bad idea for him to stay in the race: As I wrote today, his allies are now extensively on the record saying he’s not up for the job; any better performances he has won’t feel as revealing and important as what people saw in the debate (and Trump has every incentive to pull out of the second one); there’s the risk of other embarrassing age-related lapses and on a timetable, say, in October, that would be even less recoverable than what happened last week; and, simply and more importantly, he’s not up for the job. Kamala Harris is her own disaster, but she’s capable of being president as a matter of basic physical and mental competency. Trump would presumably be favored against her, too, but at least Democrats would be advancing someone who could reliably serve out a four-year term.