I'm going to have to disagree on one point. Christian voters do not predominantly vote GOP. Certain segments of Christianity in the US do (evangelical Protestants mostly), but really that's only been in the last 20 years or so. Evangelicals also overwhelming voted for Jimmy Carter, a Democrat. Now throw in other groups like Catholic, Episcopalian, and other mainline to liberal denominations, and the party breakdown is much more even. Especially with Catholics, as they are a weird bunch to pin down politically because of their traditional support for both social justice issues like poverty associated with modern liberal ideology and stances against abortion associated with conservative ideology. Hence such voter populations are often split. You can look on the Pew Research Center website for more info.