I'm really sick of comparisons like these. I don't appreciate smug, self-righteous political operatives trying to tell me (through innuendo) that atheists vote Democratic and that the Republican party is the "party of God". Enough of this garbage.
The is Pew Research data. I believe they are "political operatives" but Pew, like so many liberal groups, tries to maintain a facade of non-partisanship (why the left does this would make an interesting thread in itself). So if anyone here is saying the GOP is the "party of God" it is the Democrat party itself. You won't find many Republicans working for Pew.
The person who has dealt with the religious vote more than anyone else in the last three election cycles is Stanley Greenberg--Bill Clinton's pollster. Greenberg is married to Rosa DeLauro (D-CT). Greenberg's analysis of the religious vote in the 2004 electon, stunned the Democratic party and led to such things as Nancy Pelosi and 54 other Catholic House Democrats penning a statement about how important religion is to them. Greenberg's number crunching also led to Jim Wallis' return from obscurity (after being disgraced by his apologies for Soviet totalitarianism during the Cold War). Greenberg's analysis lead, in fact, to Barack Obama and the liberal media discussing Senator Obama's faith in some depth. It might even been the deciding factor in the party selecting Obama to run for President.
That is nothing new in American politics however. Thomas Jefferson was slammed for being a liberal Christian. In response, he allied himself with Baptists and hired the Rev. David Allen to preach sermons supporting his reelection in the heart of Congregationalist Federalist Connecticut. Alan was quite the character. He believed that if people in D.C. and New Haven built docks and warehouses for them, Jews would come in ships to America and that, along with the reelection of Thomas Jefferson, would bring about the Second Coming of Jesus Christ.
Aside from all that, look on the positive. This "diversity" in the party gives Hillary Clinton, Barack Obama, Ted Kennedy, Robert Byrd, Alcee Hastings, Kate Michelman, Tammy Baldwin and other Christian Democrats a perfect opportunity to "reach out" and fulfill the Great Commission in Matthew 28:16-20. Be something if they were able to turn the party's largest donor (the largest donor to any political party in American history), George Soros, to the faith. Last I read he is still referring to himself as an atheist.