There's a simple way to measure this. As Catholics move into Protestant denominations (or vise versa) does that body vote more / less conservative?
This may help:
Religiously unaffiliated voters - the fastest growing block - 61% identified with or leaned toward the Democratic Party, versus 27% for Republicans. - http://www.pewforum.org/Politics-and-Elections/Trends-in-Party-Identification-of-Religious-Groups-affiliation.aspx
65% of Catholics supported a tax increase for the wealthiest Americans in 2006, up from 52 percent in 2002. Majorities of Catholics support issues traditionally considered planks of the Democratic Party platform: universal healthcare, pro-labor policies, access to abortion, and social welfare programs for the poor. http://cara.georgetown.edu/NewsandPress/PressReleases/pr061808.pdf
10% of Evangelical Protestants reside in the NE, 23% in the Midwest, 50% in the South, and 17% in the West. Catholics: 29% NE, 24% Midwest, 24% in the South, 23% in the West. “Muslim Americans: Middle Class and Mostly Mainstream,” Pew Research Center, 2007. http://religions.pewforum.org/comparisons#
The population of Massachusetts ranks as the most liberal, with Boston and Cambridge being the most liberal large cities (100,000 or more), followed by California. http://www.epodunk.com/top10/liberal/index.html
The 16 most Catholic states contain 24 of the most liberal cities. Excluding (Maryland 26th), predominately Roman Catholic states contain all but one (Seattle WA) of the 30 most liberal cities. Of states in which S. Baptists are the single largest denomination none (of the 30 cities) were found. (the term “liberal” being defined according to individual contributions to PACs, election returns and the number of homosexual households: http://www.epodunk.com/top10/liberal/index.html http://www.glenmary.org/grc/RCMS_2000/Catholic_findings.htm , http://www.adherents.com/rel_USA.html.
The highest percentages of residents who describe themselves as Christian are typically in the South, including: Shreveport, LA (98%), Birmingham (96%), Charlotte (96%), Nashville (95%), Greenville, SC / Asheville, NC (94%), New Orleans (94%), Indianapolis (93%), Lexington (93%), Roanoke-Lynchburg (93%), Little Rock (92%), and Memphis (92%). http://www.barna.org/faith-spirituality/435-diversity-of-faith-in-various-us-cities
73% of the populations of Charlotte and Shreveport held scripture in high regard, versus only 27% of the residents of Providence, Rhode Island [the most Catholic state] and San Francisco [the most homosexual large city]. ^
The lowest percentages of self-identified Christians inhabited the following markets: San Francisco (68%), Portland, Oregon (71%), Portland, Maine (72%), Seattle (73%), Sacramento (73%), New York (73%), San Diego (75%), Los Angeles (75%), Boston (76%), Phoenix (78%), Miami (78%), Las Vegas (78%), and Denver (78%). Even in these cities, however, roughly three out of every four residents align with Christianity. ^
The highest percentage of souls who tended toward being atheist or agnostic were in Portland, Maine (19%), Seattle (19%), Portland, Oregon (16%), Sacramento (16%), and Spokane (16%)
Commitment to evangelism (agree strongly that a person has a responsibility to share their beliefs with others) saw the greatest percentage of endorsement by residents of Birmingham (64%) and Charlotte (54%), in contrast to residents of Providence (14%) and Boston (17%).
(See HERE for a table of casual Religious-Political relations. And HERE for correlation between faith, ideology, politics, environment, money.) TOC