Whenever a Republican rises to a position of power, they fail to accomplish the agenda that the party's activists want them to do despite all political and practical limits, and so they get tossed out and disavowed by the party's activists. So the next guy comes along, and he's even more extremist, but there's never any satisfying the base, so eventually he's out.
The problem with Trump's path to victory is that the GOP has been shrinking catastrophically, distilling itself to more and more radical elements further and further from the mainstream. It's true Trump has drawn in a lot of interest, and he may even have brought disaffected people into the party anew, but he's winning with a shrinking demographic in a collapsing party. He may have a real shot at it, if his shtick works in the general like it worked in the primaries, but I think it's more likely that he'll accelerate the party's collapse.
