Mitt Romney's Mormon faith is a major concern for many Republican primary voters -- but when it comes to a head-to-head matchup with President Barack Obama, it doesn't matter at all.

According to a new Pew Research Center poll, a third of Republicans -- and a third of all Americans, as well -- think Mormonism isn't a Christian religion, and those people are less likely to support Romney for the Republican nomination.

But if Romney does get the nomination, an overwhelming majority of Republicans, 87 percent, would vote for him over President Obama next November. That's more votes than any other candidate receives against Obama, which affirms the common perception that Romney is more electable than any of his opponents in spite of his unpopularity within the Republican Party.

In fact, white evangelical Christians, who Pew found are least likely to vote for Romney in the primaries, are actually most likely to vote for him in the general election. Just 17 percent said Romney was their first choice for the nomination, but 91 percent said they would vote for him against Obama in the general election.

The Evengelical Dynamic

This contrast may be because evangelicals tend to be conservative, which leads them to distrust Romney but also to oppose President Obama so strongly that they'll vote for essentially any Republican who challenges him.

One of the main questions has been about evangelical support for Mitt Romney, but you see that totally disappear when you get to the general election, Cary Funk, a senior researcher for Pew, told The Daily Beast. Evangelicals are the same voters who view Obama very negatively. In the head-to-head, they are just as strong for Romney as they are any other Republican candidate.

But this doesn't mean evangelical opposition to Romney in the primaries is insignificant. Evangelical Christians are a plurality of Republican voters -- more than 40 percent of Republicans who voted in the 2008 primaries were evangelicals -- and they're especially influential in early states like Iowa and South Carolina, whose primary and caucus results can set the tone for the rest of the race.

Romney's still considered the front-runner for the nomination, but Newt Gingrich is mounting a serious challenge, and Ron Paul is also gaining strength in Iowa and New Hampshire, which will hold the first votes of the primary season in January. Romney performs better than Gingrich or Paul in head-to-head matchups with Obama, but that doesn't guarantee him the nomination, especially given the depth of voters' wariness about his faith.

It's really not about Mitt. If he were a Baptist, I think he would be 10 points higher in the polls, Adam Christing, the producer of a new documentary called A Mormon President, told The Daily Beast. Some people feel like being the president is a pastoral role, that he's almost our shepherd. They seem to worry that he would not have God's phone number during the Cuban missile crisis or some other time when many of us pray. They think he's a good man, but he won't have the right connections. Evangelicals have to remember that they're not voting for a pastor, they're voting for a president.