“Bye-bye, nomination. Another one down. We’re in the midst here of discovering that this is all a hoax. The last year has established that the whole premise of man-made global warming is a hoax, and we still have presidential candidates that want to buy into it,”
That's about as explicit it can get for an elite political commentator throwing his non-support towards a candidate. What I'm interested in is how influential will that opinion be for Republican voters. Obviously Limbaugh is a popular voice on the right. But he is popular in the context of other political commentators. In the context of the entire voting population or even the population of Republican voters he listened to by a fairly small minority of people.
But a lot of the people who vote in primaries could very well listen to him and take something like this non-endorsement of Romney seriously. On the other hand, Limbaugh could just be echoing what many in the party already believe. I guess the way to test that would be to comparing Romney's polling before and after this comment.
Its difficult to know what specific things drive people's votes, especially in a primary. When you consider things like heuristics I'm not even sure a lot of people can pinpoint exactly what is driving their vote. But in this case I think it will be interesting to see how difficult a time Romney has getting the nomination considering he is disliked by some conservative elite and he is a well known name who seems to have many electable qualities. My guess would be that Limbaugh's opinion will not carry much weight with primary voters. And if there is some effect on Romney it will be because voters find out about his positions on issues. They won't just follow Limbaugh simply because he tells them to.