Trump can’t win, he might get enough support from the bat-shit-right to be the republican candidate but he’ll never get anything from the center, which is where you need to be to win in a 2 party system (c.f. UKIP and the Greens, more idealistic than either of the main two, but all they do is split the left and right vote, tory’s* won’t vote green and lefties* are unlikely to vote UKIP.)
*as distinct from the terminally stupid who’ll vote for whoever facebook/murdoch tells them too.
What will happen though will be Trump tearing all his opponents apart in attack ads. This will result in one of two (or three) things, either he’ll get the nomination, or whoever does will have to either be squeeky clean and probably a shoe in for President, or will be so broke and vilified that they won’t be able to mount a successful campaign against Clinton who will probably get the nomination with little more than token opposition.