Um. Here, have a dose of reality.
If some kind of upset causes Trump to win the nomination, the parties WON’T be fractured. We’ll still have a two-party system. They’ll be in disarray for a while, but they’ll come back together.
Are you imagining that if Trump won the election that would somehow open the way to a parliamentary system? I agree wholeheartedly that such a system would be an improvement over our two-party first-past-the-post system. However, it is insane to think that somehow this election would make that possible. It won’t. Our two-party system isn’t going away in our lifetimes. Period. Full stop.
Both parties are in trouble right now. The GOP far more so than the Democrats. But that in no respect means that they’re going to collapse and make it possible for viable third and fourth-parties. If, say, Sanders were to go Independent and split the Democratic party, at the absolute worst, you would see what happened in 1992. Everyone keeps bringing up Nader and 2000 — you need to be thinking about 1992 with Clinton, Perot, and Bush. It is much more relevant, as Perot was a far stronger candidate and much more akin to what would be happening now if either Trump OR Bernie ran as a third party. Again, at worst . . . nothing. The parties would pick themselves up, dust themselves off, and it would be business as usual.