David Freddoso on NRO lays out a complicated but compelling scenario in which the Republican primary process might not yield a presumptive nominee:

Convention Wisdom:
A Minneapolis floor fight is not so far-fetched.

I speculated on this possibility in brief a few weeks ago (here and here).

Moreover, I agree with Freddoso that a meaningful and/or raucous convention could be a great advantage to the Grand Old Party.

UPDATE: Fodder for a future post perhaps, but is has also occurred to me recently that an inconclusive primary season might tempt the relevant players to make a deal (or alliance) during the long interval following the voting but before the convention begins.