Basically, a lot of the conservative base was disappointed when Romney lost -- and when John McCain lost the general election, they complained that the RINOs foisted an excessively moderate nominee on them. I distinctly remember acquaintances of mine complaining that if they just would've listened to Rush Limbaugh and nominated Romney the Republicans would've won. Some of those people were Romney donors three years later.
For the talk-radio types to insist now, as Romney falls behind in the polls, that the moderates have saddled them with a candidate who can't win is absurd. Their endorsements of four years ago don't bind them to Romney forever. They were perfectly within their rights to back another candidate this cycle. But having insisted that Romney could beat Obama in 2008, they can't very well claim that he couldn't do so this year, when Obama and the Democrats are much more vulnerable. Nor can they claim that Romney isn't sufficiently conservative to be a good nominee, having already praised him effusively as a standard bearer who embodies all the most important parts of conservatism, really and truly feeling them in his heart. Of course, it's possible that they were just saying things they didn't believe back then on behalf of the Romney campaign.
Whether considered judgment or dishonest hackery explained their 2007 praise for Romney, it is that very praise that won him considerable support in the rank-and-file and next-in-line status in the GOP. It isn't surprising that some of these figures are trying to assign blame elsewhere as the possibility of a Romney loss sends waves of fear through the right, but they're as responsible for putting Romney in this position as anyone, and certainly more responsible than the center-right pundits on whom they try to blame everything that goes wrong in the Republican Party.