Of course, there is a “Catholic Vote” - in the literal, demographic sense. Catholics vote. Their votes can then be counted and compared with those of other groups. Drawing interesting or useful conclusions from such numbers, however, may be more problematic.
Who constitutes the “Catholic vote”? Are the Catholics in question self-defined or otherwise defined? Is the identification broadly ethnic or communal or is it more narrowly a matter of religious belief and/or observance? And to what extent does a voter’s Catholicism (be it an ethnic or communal identity or a reflection of religious belief and practice) actually influence his or her choice?
The fact is that Catholic voting patterns seem generally to mirror those of the general voting population. Thus, in 2008 Barack Obama beat John McCain among Catholics 54%-47%, just a bit better than his overall margin. Likewise, in 2004 George W. Bush beat John Kerry (the first Catholic nominee since 1960) 52%-47%, again just marginally different from the general 51%-48% breakdown. If Catholic voters represent a sort of subset of the general electorate that somehow manages to mirror it almost perfectly, that’s interesting. But the most plausible interpretation may be that Catholics just aren’t all that different from the rest of the country. Nor should that be much of a surprise, given how the American Catholic population spans the social spectrum. It’s been decades since most Catholics lived in Catholic enclaves and studied, socialized, and married mainly within those enclaves. Apart (perhaps) from some particular religious beliefs and practices, they are now indistinguishable from other Americans.
That raises other questions – like whether Catholic beliefs and practices really are all that distinct and, if so, why they don’t have a more evident impact on voting patterns. Even back when Catholics certainly seemed so much more distinctive, even then it was not clear if there was a specifically religious explanation of Catholic voting patterns - as opposed to socio-economic status and historical traditions. (The old idea that people tended to vote as they fought or would have fought in the Civil War was sufficient, for example, to explain most urban Catholics’ attachment to the Democratic Party). As for the role of religious doctrine, one might recall the saying (apparently once quoted by JFK), “We get our religion from Rome, but our politics from home.”
Here the more general recent research on religious voters seems relevant. What researchers call the “God gap” suggests something very new in American history – that those who attend religious services more frequently are more likely to vote Republican while those who attend religious services less (or not at all) seem more likely to vote Democratic. Presumably, this has its roots in the familiar historical process by which the Democratic party in the 1970s moved from being moderately pro-life to being ideologically pro-choice and the Republican party followed suit by moving from being moderately pro-choice to being ideologically pro-life – processes which have also resulted in the philosophical narrowing of both parties and the gradual elimination of teach party’s more “moderate” elements.
What’s happening with many (but not all) religious voters, I think, has been an ideological reformation in order to reduce political cognitive dissonance. Most political questions, most matters of public policy, are not readily reducible to religious principles. Whether, for example, taxes should be higher or lower is not a matter to which religion or theology offers an obvious answer. There is no distinctly religious reason, therefore, why religious voters should prefer either party’s economic ideas, let alone invest them with moral significance. If, however, such voters have gotten used to identifying with a particular party’s positions on moral matters, then over time I think they begin to adopt that party’s other unrelated positions, and (since their framework has become an ideological-moral one) they start to invest such positions with quasi-religious import. In the process, of course, this further polarizes the parties and political discourse.
All of which seems to me to be more interesting and also in my opinion explains a lot more about what is actually going on than old-fashioned denominational voting block analyses.