Choosing politicians because of their religion isn't so crazy. I mean- in most Arabian countries the leaders are Islamic. In Israel the leaders are usually Jewish. It happens for most countries, and seeing as 80% of America is Christian they probably would vote for a leader of the same faith. It's usually because the they know the leader will have the same values as them; for instance- a republican Christian will undoughtably stand for keeping old traditions.
So I'd go for a bit of religion, but mostly whether they were good enough. There are so many qualified politicians, but most of them are crap.