Gallup's final survey conducted before the 2004 election estimated that 63% of voters who attended church weekly or almost every week voted for Bush; 37% voted for Kerry. Sixty percent of those who seldom or never attended church indicated a vote choice for Kerry; 40% voted for Bush. The same directional patterns have been observed between self-reported importance of religion and vote choice. http://www.gallup.com/poll/16381/Church-Attendance-Party-Identification.aspx
Barack Obama has made no headway among white evangelical Protestants who attend church at least once a week; just 17% of this group supports him. By contrast, 37% of white evangelicals who attend services less frequently support Obama. Similarly, while Obama has made gains among Catholics overall, he runs even with John McCain among observant white Catholics (45% to 45%). He now has a clear lead among white Catholics who attend Mass less frequently (53% to 38%). http://www.pewforum.org/2008/10/23/how-church-attendance-affects-religious-voting-patterns/
I guess this could account for the fact Democrats are more hostile to traditional Christian values—pro-life values, marriage, hard work, legal immigration--if they can just get enough Christians to stop going to church, think of the vote gain!
And an opinion piece about the black church and voting: Many people call for the separation of church and politics. However, within the black community, the two cannot be separated. For this reason, my research looks at how African American congregants behave after hearing their pastors, and the church itself, preach conservative values on social issues, but yet, advance notions of voting for whoever is on the Democratic ticket, claiming the party of the left is the best way to advance the interests of the black community. This paradox is important because black churches are more than spiritual gathering places, they are power centers within the black community. For this reason, black churches have power – socially, economically, and politically. The political power of the church shows in the pulpit when pastors allow candidates to speak or advocate on behalf of a candidate or party. When looking at the structure of a black church, the public face of any black church is the pastor, and the pastor is seen as a cue-giver. With that said, this study is important because it has serious implications for the future of the Democratic Party. This is because scholars note African Americans are at a standstill between supporting a party which wants nothing to do with them and a party which takes them for granted. With pastors being cue-givers, they could become middle man to voters and candidates. This study is both qualitative and quantitative. http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2524069