Actually, if they aren't Christian (thereby believing in creationism) its a problem for the candidate. Can they also believe in evolution, sure, but they must be a Christian. As that is what the majority of the country believes in, and will vote for.

There are several hoax emails going around about Obama and how he is actually a Muslim. Personally I wouldn't care if he was, there are plenty of sensible qualified Muslims. I also wouldn't care if they were agnostic or any other belief. However, how I feel about it isn't what gets a person elected.

Why is it such a big deal in the election. Well depending on how strict their belief is can affect many other issues at hand. Right to Choose (Roe v. Wade), funding for scientific agencies, funding for educational programs that teach evolution. Many of these programs have been cut or reduced during the Bush anomaly (stem cell research). It also affects who gets appointed to the supreme court, and that will affect the end decision of major cases that are heard before it.