Now, I am not a fan of McCain (and that is a GROSS understatement) but wasn't he born on a base or other soil considered U.S. soil in Panama? That would make him eligible via the birth issue.
Other than that, I don't think children of American parents born overseas are eligible. I'm sure someone will correct if I am wrong, and I hope that happens in case my understanding is mistaken.
I was born on a U.S. Army base in Germany. Because my Dad was born and raised in the U.S. and my Mom by that time had become a naturalized U.S. Citizen, I am a U.S. Citizen.