So here's a fun problem that Trump couldn't have fixed post-convention. Even if he pivoted and went super presidential, and planned to actually try at the debates and whatnot, he'd still be super fucked thanks to his complete lack of good surrogates.
All of the ones he has are washouts. Giuliani, Christie, Pence, etc... all have no political future left to them, and that's why they don't mind shacking up at Trump Tower to squeeze what they can out of this. If Trump actually wanted to drop back for a week and do debate prep, who the hell is going to stand in his place for a week? Who could give speeches and hold rallies like Michelle and Obama? Who could go on the talk shows and light up the anchors and the Clinton surrogates with sharp campaigning?
They've got no bench, and even if Trump fixed himself, he'd still be one guy trying to win a game of football by himself. This election is going to be a great case study for a lot of different strategies that most campaigns just do as a habit. We've talked a lot about ground game, but this total lack of campaign surrogates is another serious problem. You simply can't be everywhere at once, and if you piss off the party of established (elected) officials, then you're just hurting yourself for no reason.