The Pew Research Center for the People and the Press says that religious people tend to vote Republican and non-religious people tend to vote Democratic.
Pew is a respectable organization that does a lot of good work, but I have a problem with this particular report (
The 2004 Political Landscape: Part 8, Religion in American Life).
The poll is based on the premise that "religious" people believe three particular doctrines, and that those who don't believe one or all of those doctrines are "less religious." The three doctrines are belief in God, belief in Judgment Day, and belief in the importance of prayer.
America remains an intensely religious nation and, if anything, the trend since the late 1980s has been toward stronger religious belief. Eight-in-ten Americans (81%) say that prayer is an important part of their daily lives, and just as many believe there will be a Judgment Day when people will be called before God to answer for their sins. Even more people (87%) agree with the statement "I never doubt the existence of God."
The implication is that people who don't go along with ALL these dogmas are not religious, which is of course nonsense. People who believe in all three doctrines might be defined as "conservative monotheists," but there are many intensely religious LIBERAL Christians who don't believe in a literal Judgment Day. And there are religions not based on belief in God, and a few religions that don't pray.
The Pew report continues:
Religious commitment has increased substantially among self-identified conservatives (81% agree with all three statements on faith and belief, compared with 73% in 1987-88). Liberals, on the other hand, have become somewhat less religiously oriented. Just over half of self-identified liberals (54%) agree with all three religious statements, down from 59% fifteen years ago.
In other words, Pew has decided that conservative monotheism is the One True and Only Religion. There are devoutly religious liberal and progressive monotheists who don't believe in a literal Judgment Day. According to Pew, however, these people are not devoutly religious liberal people, but actually less religious than conservative monotheists who do believe in a literal Judgment Day (and, unremarkably, are political conservatives as well).
Pew has discovered that conservatives are conservatives and liberals are not conservatives. Wow.
Pew also finds that "religious" people are more likely to vote Republican, whereas "non-religious" (as they define it) people are more likely to vote Democratic.
More commentary here.