I have no doubt 0bamy was born Muslim (as heredity goes) and denied his faith. But if his mother was a US citizen I don't see how he cannot be?
the laws in effect at the time (you know sometimes you have to thread the needle to understand how a law applies to the facts) might well be construed to prove he was not a legal natural born citizen at the time of his birth.
Also, by getting the story out there, and planting the seed that he might not be a bona fide natural born citizen, taken together with his questionable radical associations, should be able to do some collateral damage for voters in the mushy middle.
There was a thread that pointed out that the 'year' he was born is important because during that time the law was not automatic for their kids born out of the country (like Africa) to be 'automatic' citizens.