Remember, Donald Trump truly believes that the only way he can lose the election is if the other side "steals" it from him. The logical extrapolation of this kind of thinking is that, "stolen" election aside, in Donald Trump's mind, he's already won the election. One can extrapolate further, then, that Donald Trump does not believe that he needs to win any additional votes, nor do any campaigning, nor worry even in the slightest about any self-imposed threats to his victory. After all, the victory is already his ("unless they cheat").
So, if the election is slipping away from Donald, he's mentally, emotionally, cognitively incapable of being aware of it.
If things are trending away from him, I'd hate to be one of his campaign staff who know they can never confront Donald Trump about his need to appeal to more voters, when in his nutty head he's already won. So, instead he'll once again be surrounded by a bunch of "yes men" (and women) who will tell him how wonderful he is doing, right up through election night.