There are two – no, three – things to consider here. One is taqiyya. Was he indoctrinated sufficiently for this to be a legitimate concern? No answer.
Second concern is whether muslims consider him to be apostate if he’s legitimately Christian. If he’s apostate, he’s a target – death is the penalty for leaving the muslim religion, although some consideration is given if he left islam as a child. When did he convert to Christianity? Granted that presidents are well protected, but wouldn’t it have some serious bearing on any interactions with muslim countries?
Lastly, given that his father and his step-father were muslim, and his mother twice married muslims, doesn’t it follow that he is more likely to consider islamic intentions to bring the US within the islamic influence with a more concilliatory attitude than would virtually any Christian leader?

And then there’s that whole Odinga thing…that does not bode well for the US if he should happen to attain the presidency.

All of this quite in addition to the fact that he’s a blinkin’ socialist.