Nominal religion is a funny thing. It can change with circumstances. I had students on the Navajo who were Christians when the bicycle tires were flat on a Sunday but who held traditional Navajo beliefs when the tires weren't flat. Obviously, they enjoyed riding the bicycles more than they enjoyed going to church.
Christianity was superimposed on the beliefs of a lot of native people. From what I saw in Africa and on the Navajo, religion was a combination of native beliefs and newly introduced beliefs.
Obama has said that he has attended the same Christian church for twenty years. If that is true, why should anyone presume to think that he is a Muslim. Sure, his background is mixed and his beliefs probably reflect that. So what?
Does that make him a threat to you?