Well, I can't say what is McCain thinking, but in his place I will regret.
Maybe not because of electoral puropuses, as he was going, for a number of reasons (like economy, George W. Bush and republican fatique) to lose, but with more credible running-mate (as you know I'm not supporter of Republican Party, but I can say there were much more credible and able possibilities, such as Huntsman, Crist or if he really wanted to pick a woman above all someone like Hutchison or Snowe) he'd do better.
McCain really should regret because now, despite his all previous accomplishment (which I can't deny him, in fact until 2004 he was one of the hanbdful Republicans I've respected
) he is going down with history as a man who wanted to place immature and irresponsible (as her resignation showed) provincional, unexperienced governor heartbeat away from the button.
Oh yes, that';s something to regret!