It's hard to believe that Trump could be in it for any reasonable reasons.......but also to just DO it for "fun".
I really do think the reason he's done so well (if you can call it that), is it should tell us how many people in this country are short-sighted and obnoxious and rude. Trump is a narcissistic bully and his obnoxious/uninformed/make-reality-up-as-you-go behavior has given lots of obnoxious people the green light to continue to act that way. I'm ashamed that politics have gotten to this.
I think Hillary will win by a larger margin than expected. I'm hoping that the quiet/sensible people will show up at the polls.
I honestly think Trump is a mental case. The psyche classes in colleges should use him as a case study in personality disorder, among other likely diagnoses.