The latest one to smell weakness and take a whack is Paul Ryan:

Ryan, the chairman of the House Budget Committee and a leading GOP voice on fiscal matters, said that while he has not studied in depth the effects of the program — instituted by then-Gov. Mitt Romney (R) — it is having an adverse impact on the Massachusetts healthcare system. 
"It's not that dissimilar to ObamaCare. And you probably know I'm not a big fan of ObamaCare," he told reporters at a breakfast organized by the conservative American Spectator and Americans for Tax Reform.

Ryan also takes what I perceive to be a not very subtle jab:

As for whom he might endorse, Ryan said he has not made up his mind, but he said the eventual nominee must have a substantial understanding of major issues. 
"To me, what matters most is somebody that really has conviction in their heart and their mind on these core principles," he said. "We can't just give it to, you know, the next person in line or a personality contest. We will lose a personality contest. We will win an ideas contest."

Romney comes closest to "next in line." And it's true that, at the end of 2008, he seemed like the party's standard-bearer, and his Massachusetts health care plan was not considered the Death of Freedom. But the pack has turned on him.