On the one hand I can understand it. The President is the Chief Executive for the country, it's #1 representative. So, I can understand why many who believe America to be a Christian nation (by virtue of Christianity being the nation's #1 religion not to mention that American was founded on the Christian faith) would expect their nation's President to be of the Christian faith in some capacity and, as such, would in some capacity lead the country along lines that walk the path of the Christian faith. But fact is, it's not his responsibility to be the "leader of the faith". It's why each President appoints his own Priest or Pastor or defers to the Pope or some other prominent religious leader of the faith for religious guidance.