So here's how I see this now, (and keep in mind I have been disastrously wrong about this campaign so far every step of the way- but then so has just about everybody else.):
Back in 2011-12 it was possible for the conservative voters to defeat Mitt Romney, whom they despised, but they couldn't coalesce behind one candidate. By the time the actual voting came around, there was Newt Gingrich and Rick Santorum, neither one a stellar choice. Still, I believe that if one of those two had gotten out early and backed the other, the final result might have been different. But it was not to be: both Gingrich and Santorum had too much ego to quit, and they split the vote between them, which helped Romney.
This time around, it's the reverse, and it's the non-establishment candidate (Trump) who is taking advantage of the fact that the establishment can't coalesce behind one guy. If, as I suspect, Ben Carson bows out after the first few states, along with Huckabee (and maybe even Cruz) that's going to make it even more difficult for the establishment to defeat Trump. They need to choose, and choose quickly, between Bush, Rubio, Kasich, and Christie. That is their only shot to prevent the unthinkable calamity of a Trump victory.
Of these 4, Rubio is the strongest. But I don't know if Jeb Bush would be willing to quit the race and endorse Rubio. If he doesn't, Trump could pull this out.