One defense of the proposition that Mitt Romney can win the GOP nomination holds that Republicans accepted his health care position last time around. Will Wilkinson argues that this is precisely what makes conservatives so hostile to him now:

Mr Romney is infamous for his opportunistic waffling on policy, but in his principled refusal to flip-flop on Masscare he has become an intolerable living embodiment of the institutional right's incoherence on health-care reform. Mr Romney's very presence on the national scene reminds conservative editorialists of the fact that Obamacare, a policy they have demonised as incipient tyrannical socialism, differs little from policies many prominent conservatives once endorsed. The cognitive dissonance is too great to bear. So conservative opinionmakers are left with a choice: admit that individual mandates and many other features of Obamacare figured prominently in conservative health-care reform proposals just a few years ago, or throw Mr Romney to the wolves for the crime of leadership in health-care reform.

Wilkinson notes at the end that Romney may yet plug his way through to the nomination. I consider that highly unlikely, but you never know.