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Is there any point at which he just starts looking whiney to his base?
No. His various flaws seem to make him more relatable, in their eyes, bitter resentment of an establishment he feels despises and conspires against him possibly most of all. Some of them are from social groups that the establishment really does neglect, whereas he's only an outcast because he's so noxious. Plenty of rich, entitled and nasty men have been welcomed into U.S. high society over the low bar of not being quite as publicly toxic as Trump, so he has little in common with most of his base. But his petulance seems to resonate with them.
The Republicans have been preparing to fix this election for the past three years, he's going to trust that they've prepared properly and will dispute the result before the election is even held, and continue to do so long after it has finished if it doesn't go in his favour.