From a pure tactics perspective, I'd like to point out that the basic R/D split is remarkably close to 50/50. When McCain decided on Palin as VP, he solidified support from the religious right -- who were going to vote for him anyway -- and pushed away the more liberal wing of his party. That's a major mistake right there, and it's another one of those "what consequences come about from these details?" failures.

Taking a centrist VP might have kept McCain more competitive.