I don't think anyone is really going to argue that he's not a "natural-born" citizen. Yeah, it would be nice if that had been specified in law, and I imagine that this situation might instigate legislation to that effect, but I don't think anyone's really going to argue that a man born on a US military base to two US citizens isn't qualified as a "natural-born" citizen.

Not that I wouldn't like to see McCain ousted from the election.