Writing at The New Republic, Ed Kilgore contests the oft-mentioned idea that there is a distinguishable "Catholic vote" that is mobilized by issues like birth control:
The more you look at the numbers, the idea that there is some identifiable Catholic vote in America, ready to be mobilized, begins to fade towards irrelevance. In the 2000, 2004, and 2008 presidential elections, Catholics voted within a couple of percentage points of the electorate as a whole. […]
The idea that Catholics no longer behave self-consciously as "Catholics" on hot-button issues reflects the broader reality that they have become hard to distinguish from other Americans in their political behavior.
The fight over birth control coverage in the Affordable Care Act has led to a lot of prognostication about the fate of the so-called "Catholic vote." Republican strategists believe that Catholics are now ripe for the picking, and liberals like Time's Amy Sullivan see the administration's actions as a recipe for alienating said voters. But, as Kilgore points out, the numbers don't support the idea of an identifiable Catholic bloc. Indeed, the Catholic vote tracks the overrall vote so closely that, if you were to take a random sample of Catholics and compare their preferences to a random sample of all voters, the results would probably be close, if not indistinguishable.
Where there is a distinguishable Catholic vote, it's with conservative Catholics. But even there, they don't vote in ways that are substantially different from conservatives as a whole. In other words, the most relevant thing about conservative Catholics is that they're conservative, not Catholic.
None of this is to say that a identifiable Catholic vote is impossible-if Obama were to denounce the Pope as the Whore of Babylon and handmaiden to the Antichrist, then Catholics would probably mobilize around their religious beliefs in response to open bigotry. But barring that, we can expect Catholic voters to behave like every other voter. If President Obama wins reelection in November, he'll almost certainly do so with a majority of Catholics at his side, and if he loses, then odds are good that the Republican nominee picked up the "Catholic vote."