A president upholds the constitution, not his or her personal moral or religious view. I would quote John F. Kennedy at her. Check out some of his relevant quotes from http://www.positiveatheism.org/hist/quotes/jfk.htm ... here are a couple of samples ...
I would not look with favor upon a President working to subvert the First Amendment's guarantees of religious liberty ... Neither do I look with favor upon those who would work to subvert Article VI of the Constitution by requiring a religious test -- even by indirection.
-- John F Kennedy, address to the Ministerial Association of Greater Houston, September 12, 1960, from Albert J Menendez and Edd Doerr, The Great Quotations on Religious Freedom
Whatever one's religion in his private life may be, for the officeholder, nothing takes precedence over his oath to uphold the Constitution and all its parts -- including the First Amendment and the strict separation of church and state.
-- John F Kennedy, Interview, Look, March 3, 1959, from Albert J Menendez and Edd Doerr, The Great Quotations on Religious Freedom
Kennedy was considered unelectable by many because he was catholic. He had to make it clear he wasn't going to be the hand puppet of the pope before people would consider voting for him. I remember that his religion was a huge issue at the time. Very similar to Romney and mormonism right now.
Christians do not own morality. They sport one of many versions, most of which are compatible with each other. Morality has social sources, and as researchers are finding out, morality also has biological sources. We humans have the ability to cooperate for genetic reasons as well as social ones.
The irony of course is that christians take credit for our biological propensities while denying evolution. Cute.
Christians drowned "witches" with exactly the same righteousness that they use today to claim that they are moral. And christians in Africa are burning witches in this century with the same glee. Once any group lays claim to moral rectitude and excludes external feedback, everything goes downhill no matter what group it is. Christians can lay claim to morals all they want, their history demonstrates the inherent flaws of any monoculture.
If this was 1511, every atheist on this forum would be in danger of being burned at the stake. I'm pretty sure the social progress made since then has been the product of multiple cultures and multiple belief (and nonbelief) systems, rather one group being really really good.
The christian treatment of native peoples around the world kind of excludes them from laying claim to perfection. And their take on social issues such as abortion and homosexuality proves that they still ride their high horse and don't give a f*ck about who they trample.