Which he's demonstrated having neither.
I think this is the key. The Republicans finally pull off the trifecta to run the table (House, Senate, and White House) and Trump chooses to abandon that in favor of working with Democrats to secure votes he shouldn't need?
I think that would spell doom with his base with very little upside - even if they work with him selectively on center-leftist initiatives he's fond of, Democrats ultimately think he's a moron, a bigot, and a wannabe tyrant. They'll never coalesce into the support he needs if he loses his GOP base.
I don't count him out per se, but I just don't see the people he vanquished as all that impressive in the first place. I was completely surprised he won the nomination, but the field of competition was not exactly sterling.
Re: beating the Clinton machine: again, I don't think in 2016 there was much of a machine. Influence in the party? Yes, too much, hence the DNC clearing a path for her. But an incredibly flawed candidate (she ain't him) and a tired and galactically hypocritical message wasn't very impressive to start with. I think any generic Republican would have probably won.