Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I even say who wrote them. If you have more recent summaries to add to this collection, send them my way I guess. Sorry for the ads; they cover the costs of keeping this online.
Guth, Kellstedt, Smidt, and Green. 2005. Religious mobilization in the 2004 presidential election. Presented at the Annual Meeting of the APSA, September 1-4, 2005..
It's not just a Protestant/Catholic or Religious/Nonreligious divide. You need to sort people properly based not only on Evangelical vs Mainline Protestant and Catholic, but also based on whether they belong to a Modernist, Traditionalist, or Centrist faction of those traditions.
When classified properly, religion has strong predictive power.
The major religious traditions have been polarized into liberal and conservative factions (based on theological, social, and cultural conflicts) Three ways of differing:
Research by the same authors
Research on similar subjects