The news is all abuzz today over the fact that Santorum "lost" the Catholic vote in the primaries last night. It's a construction that assumes that it was his to lose, and is based in one of the most pernecious myths of the Beltway media, which is that America is a sectarian society where "people of faith" not only vote according to religious guidelines, but according to those set by the loudest sectarians amongst them. Thus, you get claims that Obama is going to lose the "Jewish vote" because, I dunno, something about Israel, even though he really hasn't done a damn thing to hurt Israel. And now there's a growing adherence to the nonsensical belief that Catholics are a voting bloc, and one that votes primarily based on what a bunch of right wing celibates who spend all their time on TV denouncing vaginas think. The only group that doesn't get this treatment is mainline Protestants, because as the mainstream media doesn't tend to think of "white" as a race so much as a baseline, so it thinks of mainline Protestantism as the norm by which you measure others against. (On that basis alone, I enjoyed Santorum saying mainline Protestants aren't real Christians, because it actually jolted the media into realizing that various Protestants are also religious groups, just like Jews, Catholics, evangelicals, and Mormons.)
But really, this nonsense about the "Catholic vote" has got to stop. There's literally no evidence for such a thing. Most Catholics are pro-choice and use birth control, and they do so in roughly the same numbers as non-Catholics. In fact, they're indistinguishable from the public at large in their voting habits. There's perhaps a slim chance that some of them were moved against Santorum by the JFK comment, but honestly, I'm skeptical. The reason is that we're talking about a Repubilcan primary. I guarantee their identity as Republicans was a bigger factor for Catholic Republicans voting in the primary than their loyalty to the only Catholic President.
Ironically, Rick Santorum is a perfect example of why this supposition that Catholics are following Vatican marching orders when they vote is just completely off-base. Santorum's hardline stance on contraception is presumed, incorrectly, to stem from his devotion. In fact, like with other conservative Catholics, the Pope just provides cover for already-existing misogyny. That is to say, they hated women first and used faith to rationalize it second. You can tell this, because the Pope has lots of other opinions on stuff besides contraception, and Santorum ignores all of it. Juan Cole put together a list of ten Catholic teachings that Santorum rejects while pretending to be a hapless warrior for Catholic Jesus. Santorum has gone against the church on the issues of the Iraq War, universal health care, the death penalty, welfare, the minimum wage, union organizing, and immigration. Interestingly, not only does Santorum reject the church when it comes to these political matters, he also is a cafeteria Catholic on issues of religious questions. For instance, the Catholic Church accepts the theory of evolution and teaches that their god guided the process. Santorum rejects church teachings on this. In fact, not only does the Catholic Church accept evolution, but they are like most religions in this. Really, it's only evangelical Christians that hold that one must reject evolution as a part of their faith; Jews, mainline Protestants, Muslims, etc. by and large accept the theory as not in conflict with their religious beliefs.
The point isn't to say that Santorum is more or less Catholic than other Catholics who may agree with church teachings far more than he (while mostly rejecting the contraception nonsense as the medieval misogyny that it is). The point is that Catholics are a diverse group, politically speaking, and their faith has very little bearing on how they lean. Race, class, geography, personality, etc. all have more influence. In fact, as the example of Santorum shows, there's something of a cultural conflict between the markers of wingnuttery and Catholicism, and so Catholics who want to go full wingnut end up looking and sounding more like evangelicals. Which, in turn, means the notion that a Bible thumper like Santorum is going to make cultural appeals to Catholic voters sound even sillier, since he doesn't really come across as the average Catholic, insofar as there even is such a thing. I bet, if you surveyed people, a substantial number would think he's evangelical. Possibly even a majority.
By the way, that is one religious group that does have a predictable vote: evangelical Christians. While a minority are more liberal, by and large, most are fundamentalists. The whole point of being a fundamentalist is that it gives godly rationalizations to your conservative leanings, and so this isn't surprising.