He is a crypto-Muslim. His politics will be no doubt benefit the most radical Muslims worldwide, but he will do it not that in-your-face style like putting his oath on the Koran. He will use the Bible. No doubt. He is trying to fool us.
I agree, he would definitely use a Bible. But check this out FWIW. When you get to the link, keep clicking on the small arrow at the right end of the picture stream until you get to the very last photo (it includes Obambi.) The middle guy appears to be the head of Project Islamic HOPE (Helping Oppressed People Everywhere).