The Senate voted 51-47 to not repeal the ACA. That's a really slim vote that could have been closer if Republicans would have picked up a few more seats.
Two of the most popular candidates for Senate in the last election were Sharon Angle, who was running for Harry Reid's seat in Nevada, and Christine O'Donnell, who was running for Joe Biden's seat in Rhode Island. Both were tea party candidates who became popular for all of the crazy stuff they said.
Both candidates upset the Republican backed candidate who was polling well against the Democrat challengers. I don't remember how well the Rep was doing against Reid. That's in part because Reid scared off a lot of challengers. But considering Angle herself gave him a close race its not too difficult to imagine a less radical candidate making it even closer. I do remember that the candidate O'Donnell upset was a prohibitive favorite to win against the Democrat. But O'Donnell's victory virtually assured the Dem would win.
Assuming the Dems who won those seats voted against repealing the ACA, those two seats could have made the vote 49-49. That doesn't mean the ACA would have been repealed. If Biden was called on to break the tie he surely would have voted against repeal. And if not Obama would have vetoed it. But that would be embarrassing for Dems and Obama to have to do and it would have given the Reps about as good a victory as they could have realistically hoped for.
Republicans did nothing but embrace the tea party in the lead up to the last election. Its true that they don't control the primary process. But I think its possible that they gave credibility to the tea party and the dark horse candidates like Angle and O'Donnell. Sarah Palin, one of the most popular figures in the Republican party, endorsed both of them.
Firing up the base can serve a lot of good for your party. But not every state and district is representative of your base. And its going to be hard to get enough of those more moderate people to vote for less moderate candidates on a regular basis.