Maybe Obama is now a Christian. Maybe not. (I'm not so sure what the Rev'd Wright is preaching is actually Christianity. It sounds more like a combination of Black Liberation "theology" and Nation of Islam.)
But even if he is no longer Muslim, the recitation of the call to prayer includes the Muslim affirmation of faith.
From the point of view of a strict Islamicist, once you recite that, even once, you ARE a Muslim.
So even if he's not a Muslim, radical Islamicists can proclaim that he is, or was, one.
Which gives several alternatives: (1) by reciting the sahada, he is lying to the Muslims by convincing him that he really is < wink wink nudge nudge > "one of them"; (2) if he recites it but then retracts it, he's an apostate and the radical Islamicists believe they can kill him on the spot; (3) he is too stupid to realize that he has well and truly put his foot in it with this.
None of these alternatives are particularly appealing.
Or 4) He thinks he can play both sides of the fence and appease both Christians and Muslims.
I think stupid fits. Along with 57 states, the "bomb" on Pearl Harbor and endless other demonstrations of illiteracy. I suspect his "Harvard" education was an affirmative action sham with "social promotion" in exchange for paying the fat annual tuition. As for claiming to be a Christian, I think that is strictly for show. The Islamic madrassa formed his ethical outlook.