A person's religious beliefs will always affect their decisions to some degree or another. Bush is no different. Presidents aren't in office just to make decisions based on public opinion polls. A President is elected as a representative to make decisions for the country. Any time a person makes a personal decision, he moral beliefs come into play. Bush was elected as an active Christian, and now he's acting like one. Obviously Americans approve of Presidents making decisions that are influenced by their moral beliefs; as someone mentioned here a few weeks back, virtually every mainstream presidental candidate claims to be a Christian. If they did not, it would be a whole lot harder to get elected. IMO, Americans think that if the politician has religious beliefs, they might be a more moral candidate and "take the high road". Americans want to believe that this country always does the right thing when an action needs to be taken. If their leader appears to be concerned with doing the right thing, then it gives them as sort of peace of mind.
Personally, I don't have any problems with a politician's moral views affecting his decisions. If they start to impliment policies that enforce their religion, then we have a problem. But as I see it, there are a lot of crooked politicians out there, and higher moral standards sure wouldn't hurt.