I have zero doubt in my mind that Trump's debate prep, aside from the hours spent housebreaking him, has been spent teaching him just enough on policy to be either technically correct or sound correct but only if you're barely paying attention (which I'm sure applies to just about everyone watching). Glib answers to every policy question, zero elaboration if pressed. Looking like he has some idea of what he's talking about is about as curvy as his pitches are going to get because they can't possibly teach him the policy he needs to know to go beyond that. I suspect we'll see him basically grinding along on his verbal crutches ("It's gonna be good / great", "believe me") like training wheels the whole night. Very few "gotcha" moments based on fact, plenty of them based on appeals to the audience or the lowest common denominator.
Like we'd said many times, all he has to do is not call her a bitch and he'll be seen as presidential. If he acts like he did in the primary? I don't see how it doesn't explode in his face.