Ah, here is the money quote from Rush on the matter;

Well, it’s time, ladies and gentlemen, for the Limbaugh Rule to supplant and replace the Buckley Rule, because the Buckley Rule requires clairvoyance. The Buckley Rule requires people who can’t possibly know the outcome of anything in the middle of September to support or not support somebody based on what they think’s going to happen in early November. Christine O’Donnell can’t win, she’s 25 points down. Can’t win? If a constitutional conservative can’t win in this climate coming down from 25 points, we need to find that out, find out where we are. Why not go for it? The stakes dictate it, do they not? Here’s the Limbaugh Rule: In an election year when voters are fed up with liberalism and socialism, when voters are clearly frightened of where the hell the country is headed, vote for the most conservative Republican in the primary, period.