The Pew Center for People and the Press has come out with a solid new study (sample size 80,000) on the electorate in 2004. The full report is here:
Pew Study
It covers lots of territory. The one that strikes me, because I've discussed it before, is the growing divide between secular leaning Democrats and religous leaning Republicans. The summary table on religion and party ID is this (numbers are precentage in category identifying with a major political party):
R D
Total 29 30
Protestants 33 32
White Evangelicals 44 23
White Mainline 35 26
Black 5 68
White Catholics 30 30
Regular Attendance 33 29
Rarely Attend 25 31
Jewish 17 54
No Religion 14 28
(Incidentally, independents are less religious than either Democrats or Republicans and increasingly are polling like Democrats).
Much of this is just political conventional wisdom. Evangelical and born again Christians (a rapidly growing share of the religious pie) increasingly vote Republican. Blacks, Jews and people with no religion vote Democratic by large margins. People who attend church regularly vote more like evangelicals than those who do not.
The big bombshell, which I've been aware of for a long time, but conventional wisdom hasn't yet recognized, is that mainline Protestant white Christians tend to vote Republican by very large margins -- more strongly than regularly attending Catholics, almost as strongly as people with No Religion vote Democratic. The same people whose churches are recognize gay bishops and gay unions, exhorting members to help the poor, denouncing hate, urging racial tolerance, etc. vote with their pocket books and not with the pulpit.
Like suburban voters, who are also Republican leaning swing voters, we can have their votes, but don't, in my opinion, largely because of fear of Democratic economic policies. The Democrats don't need, and aren't going to get the Evangelical vote. But, it does need mainline Christians and Catholics.