There are only two realistic front-runners for the GOP primary right now--Donald Trump as the front-runner, with Senator Ted Cruz pulling alongside or occasionally leading by a smidge depending on what state's polls you are looking at. I'm a life-long Democrat, so this dynamic is fascinating to me: both of the candidates in the lead for the GOP nomination seem to have significant groups of people in their own party who really seem to shudder at the thought of them getting the nomination.
Now, people have been writing "Everyone Hates Ted Cruz" pieces ever since he became a senator, so I appreciate how an "Anyone But Cruz" party came about. His brash and uncompromising brand of conservatism is distinctively unhelpful in the atmosphere of the Hill, and has led long-time senators like John McCain to dub him a "wacko bird". But when the Governor of Iowa actually says out loud that he wants Cruz defeated, that's a pretty significant sign of the sheer magnitude of the Calgary-born Cruz's ability to rub people the wrong way.
On the other hand, long-time Conservative publication National Review is putting out an entire issue arguing against Donald Trump, questioning his conservative bona fides, temperament and seriousness, indicating that there is also an "Anyone But Trump" contingent that is alive and well. (And yet, probably awfully late to try to start slowing Trump's roll, now.)
As Sarah Palin's rambling endorsement the other day indicates, Donald Trump has been running on a populist trip, and has curiously picked up significant evangelical support (which Team Cruz probably by rights thought were his folks). And yet, funny old thing, the donors/establishment types are coming around to Trump.
Now, despite all this, I'm not really seeing a path for, say Marco Rubio to three, two, one his way into the lead, let alone for Bush or Kasich to suddenly take the lead. The establishment is no more.