Is Obama a Christian? Is Palin?
For an American politician to announce that he was an atheist or agnostic would cost him a lot of votes in a national election. Obama is an ambitious and successful politician. So the fact that, at an early stage in his career, Obama announced that he had become a Christian tells us very little about his actual beliefs.
The same is true of other politicians. Sarah Palin was, I suppose, the most visibly Christian of the four candidates in the most recent presidential election. That may well represent her actual beliefs. But without knowing more than I do about when she first acquired political ambitions and what her life was like before that, I have no way of telling whether she is a devout believer or a competent pretender.
We do have pretty good evidence that neither Obama nor Palin is a Muslim, however. Islam requires of its believers visible actions, such as praying four times a day and fasting during Ramadan. I think someone would have noticed.