Freedomworks is coming after you, Mitt Romney:

A top goal of the nation’s most influential national Tea Party group is to stop Mitt Romney from winning the Republican nomination for president.
Interviews with top officials at FreedomWorks, a Washington-based organizing hub for Tea Party activists around the country, revealed that much of their thinking about the 2012 election revolves around derailing the former Massachusetts governor. ...
Kibbe said in an interview that FreedomWorks has no plans at the moment to endorse an opponent of Romney’s in the primary. But others in the organization made clear they will devote considerable resources toward helping whoever emerges as the most viable Republican in the primary other than the putative front runner.

Freedomworks is a powerful and well-funded organization. What's more, it has gained a huge amount of prestige among conservatives. The right-wing political narrative is that the party was punished by voters because it abandoned its ideological principles during the Bush administration, and The People, operating through the Tea Party, forced it to regain its bearings, leading to the glorious victories of 2010. Freedomworks has claimed much of the glory of that resurgence, which gives it enormous legitimacy that leaders who arose before 2009 don't have.

I'm not saying the determined opposition of Freedomworks is by itself fatal to Romney's campaign. (Nor am I saying he has absolutely no chance -- hey, anything can happen.) But when a candidate is saddled with (and can't abandon) a position that many voters and interest groups within his coalition deem totally disqualifying, then he's in deep trouble.