2008 was lost no matter who was the nominee, but picking anyone competent (not Palin) for VP would have gotten him another point. She had the most negative impact for a VP in history.
McCain probably knew he was going to lose unless something else happened so he took a gamble on Palin to shake things up. It played out like most gambles: a loss.
His VP pick did reengage an important part of the GOP base that was prepared to sit on the sidelines. That part of the base did show up to vote, but it was way too little in the face of all the other factors swirling around those last couple of months.
