Tom Jensen of Public Policy Polling tells us that Kay Bailey Hutchison was probably toast, had she decided to run again (via Jon Chait):
Hutchison's approval rating with Republicans on our last Texas poll was just 58%. To put that number into some perspective Lisa Murkowski's approval with Republicans in January of 2010 was 77% and Mike Castle's in March of 2009 was 69%. They both started out in a much better position against their Tea Party opposition than Hutchison would have, and they both lost anyway. A poll we conducted in September of 2010 found that only 25% of Republicans in Texas would support Hutchison for renomination to 62% who preferred a 'more conservative' challenger. It's doubtful Hutchison really would have lost by that sort of margin, but she certainly would have been in deep, deep trouble had a Tea Party challenger emerged.
Jensen goes on to say that "there is pretty much no Republican incumbent immune to a challenge from the right these days," and he's absolutely right. The reason is that context is everything. Why is it that KBH fell so far with conservatives? It wasn't because she suddenly became some kind of liberal. She ran against Rick Perry for governor, and there was a campaign in which she was painted as a liberal. And though she wasn't an actual liberal, she was certainly more liberal than Rick Perry (granting that you could say the same about pretty much anybody). So now, having watched that campaign, Texas Republicans see her as pretty liberal. Everything's relative.
The events of the last couple of years have made Republican primary voters everywhere much more receptive to the argument that their incumbent senator is not conservative enough. Senators often get challenged from the fringe by obscure figures, and they are usually able to swat away these challenges. But in today's GOP, the question, "Is Senator X conservative enough?" has become for many the most important question one needs to ask, maybe the only question. And with a sufficiently extreme challenger, you can make the case that any Republican isn't conservative enough. All it really takes is a core of activists dissatisfied enough to get the ball rolling with some early attention and money for their standard-bearer, who will go around calling the senator a liberal, and before you know it, "Is Senator X too liberal for us?" becomes the question on which the primary turns.
So in 2012, it won't just be actual moderates like Dick Lugar and Olympia Snowe who will be getting primary challenges. There are going to be a number of senators challenged from the right, about whom we'll say, "How could anyone think he isn't conservative enough?"
-- Paul Waldman