Romneycare's Shadow

Chait thinks Romney's Massachusetts healthcare reform has doomed his presidential campaign:

Romney's problem on this issue isn't with independents. It's with the GOP base.

I'd also be curious to hear from some conservatives about how they see this. In 2008, nearly all of them were fine with Romney's health care plan. (National Review endorsed Romney for president.) Now, to a man, nearly all of them believe the imposition of a regulate/subsidize/mandate scheme represents one of the worst catastrophes in American history. How do they account for their dramatic change of mind? Were conservatives all simply wrong and ignorant in 2008, and now they've opened their eyes? Or is something else at work?