Mitt Romney's Mormonism and its potential to help the faith become more "mainstream" present a threat to many evangelicals, who have been seeking to point out why his faith is not Christian as one way of competing in the "marketplace for souls."

That's according to the authors of a new poll showing "intense bias" among evangelicals toward Mormons. Brett Benson, assistant professor of political science at Vanderbilt University, said the Southern evangelicals surveyed "were offended when they hear the Mormon claim that they are Christians. They become defensive and don't want to allow them that status."

Benson said that, for many, Romney's candidacy "presents a risk in allowing a Mormon to occupy a mainstream position, where they could risk losing the standing they have relative to Mormons, and that has a lot to do with this 'marketplace mentality,"' as both groups proselytize and seek to share their version of Christ's gospel with the world.

"If you can define Christianity in such a way as to exclude Mormons from that group — particularly in evangelical academic conversation — when you ask why they are unwilling to allow Mormons to have that designation, you run into this 'I just thought the club was closed' mentality.

"Both are proselytizing faiths. If you can define Christianity in such a way as to exclude them, you exclude much of your competition. That's consistent with much of the message we run in our analysis" of poll results, Benson said.

John Geer, also a political scientist and Benson's colleague on the survey at Vanderbilt, said he thinks Benson's interpretation "makes good sense, but it's not my idea." He said he believes "that's partly what's going on. There are incentives in these competitive conservative churches" to emphasize theological differences between Mormonism and historic Christianity. "They don't want the competition."

The survey sampled 1,200 Americans and another 600 Southern evangelicals so comparisons could be made between their responses.

Leaders of the Southern Baptist Convention — the largest denomination among evangelical Protestants — began publicly voicing their opinion that members of The Church of Jesus Christ of Latter-day Saints are not Christians in the mid-1990s, as the church's missionary effort produced record numbers of converts. They have continued to insist that theological differences eliminate Mormons from the "Christian" club, while Latter-day Saint leaders have steadfastly maintained they are, indeed, Christian, in the sense that they worship Jesus Christ as the head of their faith and redeemer of the world.