He's a stalking horse for the GOP, taking the wind out of Conservatives. As soon as the conservatives fold up, he'll intentionally flame out, leaving the NeoCons and Lib pubs looking 'reasonable, polite, and compromising'... watch and see.
Ugh, I knew I'd forget an option. Not that I agree with it, but a choice #4 should have been available:
4. Trump is a stalking horse for the GOPe. His real goal is to divide and confuse conservatives.