Overlooked in all of the hubbub over Wisconsin Rep. Paul Ryan's selection as the Republican vice presidential nominee -- Medicare! Ryan budget! Shirtless! -- is the fact that Ryan is a practicing Catholic.
That's potentially important this fall -- for two reasons.
First, as we have repeatedly written, the Catholic vote have proven to be perhaps the most reliable barometer of the overall national vote in a slew of recent presidential elections.
Since 1980, the candidate who won the Catholic vote also won the presidency in every election save 2000 when Al Gore narrowly edged George W. Bush among Catholics but lost nationwide. (It's a matter of debate whether that factoid makes Catholics a swing vote or simply one that moves in coordination with the mood of the national electorate.)
Here's a chart that makes those numbers plain.
Then there is the fact that the Catholic population in the country is largest in the upper Midwest, the region of the country that Ryan hails from and which is also seen as the central battleground between the two parties in the November general election.
Here's a map from the 2010 religion census detailing where Catholics live in the country:
To be clear: Simply being Catholic is no guarantee of winning the Catholic vote. Massachusetts Sen. John Kerry, a Catholic, lost the Catholic vote by five points to President George W. Bush, a Methodist.
And, Democrats note, that Catholic bishops have spoken out against the Ryan budget and that their side has a Catholic of their own in Vice President Joe Biden.
But with the Catholic vote -- and the electorate more broadly -- so closely divided heading into the fall election, small factors can make a big difference. And, it's no accident that Ryan spent Monday -- his second full day as the Republican VP nominee -- in Iowa, a state, particularly in its swing eastern region, filled with Catholics.
Keep an eye on how often -- and at what length -- Ryan talks about his Catholic faith on the campaign trail. The more he does it, the more the Romney campaign believes it can help win over the critical Catholic bellwether vote.