Isn't he also on record admitting that he was too inexperienced to run for VP in 2004? And now in 2008, with no experience gained in the interim, he's running for President? I know the Republicans are viewed as the stupid party, but even they wouldn't pass up the opportunity presented there.
Plus, his opponents just have to show this to crush his chances..
http://www.youtube.com/watch?v=2AE847UXu3Q