JoeBob,
I think that's a part of it. I think he does believe he can do a good job as POTUS, and put America back on track.
However, I also think Trump is interested in the job of President because it wins cocktail parties vs. Gates, Buffet, Ellison et al. The other billionaires might be smarter, richer, etc... but have any of them been President, meaning they're beloved by all the people (which he'll convince himself is the case)? Heck no, so they can all STFU.
Nothing could vindicate his braggadocio easier than winning the general election. It would confirm that all the stuff he thinks of himself is true, and if he doesn't win, well we're all too stupid to realize his singular awesomeness. Either way, his ego wins.
This is a well thought out business maneuver that he really cannot lose IMHO.
