Our resident religion & politics guru Mark Silk assesses the religious layout of 12 battleground states – and explains why religion will matter on Election Day.

Arizona

If Arizona is a battleground state this year, it’s because of the influx of Latinos over the past two decades. This shows up as significant growth in the number of Catholics, who over the past two decades have increased their share of the state population by 20 percent, to nearly one-third of all Arizonans and a quarter of the electorate. Latino Catholics are among the most Democratic religious groupings in the country. Add to them a comparable growth in the proportion of Nones (those who claim no religious identity) and a substantial decline in the number of Protestants, and you can understand why Arizona is no longer as safely in the Republican column as it used to be.

Colorado

The proportion of Christians, both Catholic and otherwise, has shrunk over the past two decades, while the Nones have grown apace. In 2008, this helped Obama handily win a state that had gone Republican in eight of the previous nine presidential elections. If he captures Colorado’s electoral votes again, it will be because, with the Nones and the evangelicals balancing each other out, strong support from the largely Latino Catholic community offset the Romney margin among mainline Protestants.

Florida

Since 1990, Catholics and Nones have gained bigger shares of the electorate of the Sunshine State while the Protestant proportion has dropped. This suggests a trend toward the Democrats, but the large number of Cuban-Americans in the Catholic population makes Latinos less of a Democratic constituency that they are in other states. In a sour economy, Obama will need big numbers from the Nones, the Jews, and the other non-Christians if he is to carry the state for the second time.

Iowa

After voting for Republican presidential candidates through most of its history, Iowa has gone Democratic in five of the six last races. In part this may reflect the sharp drop in the percentage of Protestants in the state—and a comparable rise in the number of Nones and those professing non-Christian faiths. This year, however, Iowa could return to the Republican fold, thanks to intensive anti-Obama advertising by the Romney campaign and its associated Super-PACs. In 2008, nearly one-third of Iowa evangelicals voted for Obama. If that number drops to the evangelical norm of 25 percent for Democratic candidates, it could turn the state red.

Michigan

Michigan has gone Democratic in the last five presidential elections, and no one will be surprised if it does so again. Not only are evangelicals a smaller share of the voting population than in neighboring Ohio, but a greater proportion of them—fully one-third, as opposed to 27 percent—voted for Barack Obama in 2008. To be sure, Mitt Romney is a native son, and son of popular governor. But he opposed the auto bailout that is Obama’s calling card in the Wolverine State.

Nevada

Mormons in eastern Nevada give Mitt Romney a leg up, but they only make up five percent of the Silver State’s population—just one-third the number of evangelicals. For his part, Obama can depend on a larger base of Nones and Latino Catholics. If the president can manage to hold on to enough mainline Protestants he will keep the state in his column.

New Hampshire

The Granite State had been trending Democratic in the 21st century until 2010, when its old-time libertarianism returned in a bluster of Tea Party enthusiasm. No battleground state has fewer evangelicals, but there are enough conservative Catholics to wave the flag of family values. If Obama manages to hang on to the state, it will be because of the Nones, who voted for him by better than three-to-one in 2008, and whose portion of the population has more than tripled over the past two decades.

North Carolina

No battleground state has a higher percentage of evangelical voters than North Carolina. In 2008, they voted John McCain over Barack Obama by a 74-25 margin, but polling in early October showed them favoring Mitt Romney over Obama by just 68-29. Add to that the possibility that some Tarheel evangelicals will decline to vote for either Obama or the Mormon candidate, and it could be Wednesday morning before we know how the state voted.

Ohio

In 2004, when George Bush carried the Buckeye State by two points, evangelicals voted for him by a margin of 76-24. Constituting 25 percent of the electorate, they provided him with a 13-point cushion. In 2008, evangelicals were up to 30 percent of Ohio voters, but they went for John McCain by only 71-27, costing him half the 52-47 margin by which he lost to Barack Obama. This year, surveys show Mitt Romney leading Obama among evangelicals by as little as 20 points. If Romney carries Ohio, it will be because evangelical activists like Ralph Reed manage to return their people to at least McCain levels of support.

Pennsylvania

In 2008, Obama did well with Protestants, not so well with Catholics in the Keystone State, but this year, the Catholics are a lot more enthusiastic about him than the Protestants are. The explanation? Catholics have come to see Obama as a traditional Democrat, and a significant number of Protestant Obama supporters have started identifying themselves as “None.” So long as Catholics don’t embrace their church’s call to see the Administration as hostile to their religion, Obama seems safe.

Virginia

Thanks to huge growth in the Washington suburbs, Virginia has a smaller proportion of evangelical voters than North Carolina, and larger proportions of mainline Protestants, Catholics, and Nones. That makes the Commonwealth more likely than the Tarheel State to end up voting for Obama.

Wisconsin

Four years ago, Barack Obama carried Catholics while losing Protestants in the Badger State. But the Catholic population of Wisconsin has been falling while the Protestant population has become more evangelical. Although Wisconsin has voted for the Democratic presidential candidate in each of the last six elections, it’s a close call in 2012, and this helps explain why.

EXPLANATION OF DATA: Most of the data in this chart were obtained from the state-by-state exit polls taken in 2008. In all but three cases (Colorado, North Carolina, and Virginia), voters were asked to provide their religious identity as Protestant, Catholic, Other, No Religion, and occasionally Jewish. In all but two cases (New Hampshire and Pennsylvania), voters were asked whether they were born-again or evangelical.

To obtain the portion of mainline Protestants, we have simply subtracted the percentage of evangelicals from the percentage of Protestants. For the three states where religious identity was not asked for, we used the percentages provided in the 2004 exit polls, which did ask.

For the distribution of evangelicals and mainliners in New Hampshire and Pennsylvania, we used the proportions provided in the North American Religion Atlas (http://www.religionatlas.org/). The LDS Church supplied the number of Mormons in Nevada, where they constitute a significant fraction of the population but a fraction that the Nevada exit poll did not register separately.