Rush Limbaugh did explain a simple concept (Rush hates McCain too, just in case you don't understand), for her to not endorse him would have been far worse, seen as ingratitude and incomprehensible pettiness on her part.
I understand that concept, most people here understand that concept, but for some reason, you and a few others can't.
It's very simple, the voters of AZ elected McCain by some 24 points, JD was a poor candidate to run against him.