Although it's disgusting that Trump won (no surprise, given the polls), if you add up all the Republican voters who didn't vote for him, nearly 70% voted against Trump. Problem is, too many candidates competing for the anti-Trump vote.
If you combine Rubio/Cruz #'s, that's 10 points more than Trump
Rubio has razor thin lead over Cruz with 99% reporting.
Bush dropped out. Who picks up his supporters? Trump or Rubio? Same question if Kasich drops out.
A challenge facing Cruz is that he's probably more of a regional candidate than Rubio. If Cruz can't dominate Southern primaries, where will he make up the difference? Likewise, he didn't sweep the evangelical voting block in SC. Yet he needs that to build on. And he needed momentum. Now Trump and Rubio have the momentum.