Reply #12: Gallop speculates that Foleygate is the reason also:

[rodeodance]

...The data reviewed here suggest that the Republicans have lost -- at least temporarily -- some of the disproportionate advantage in voting preference they have enjoyed among religious whites. This group continues to be much more likely than less religious whites or nonwhites to support the Republican candidate in their House race, and is currently as likely to support a Democrat as a Republican Congressional candidate. But, the difference between religious whites and these other two groups has narrowed somewhat as of the Oct. 6-8 poll.

One plausible explanation for the broad drop in Republican support in the most recent poll is the Mark Foley scandal in Congress. Since this situation involved issues of morality on the part of Foley, and allegations of a cover-up on the part of Republican leadership, it appears plausible that religious whites may have become disproportionately disillusioned with the Republicans and as a result lost more of their fervor for voting Republican than others in the population.