(RNS) On June 27, 1844, vigilantes cornered a man who claimed to receive messages from God and gunned him down in an Illinois jail after his arrest.

At the time of his death, Joseph Smith Jr., founder of the Church of Jesus Christ of Latter-day Saints, was an announced candidate for president of the United States.

Today, 167 years later, as two of Smith's adherents eye the nation's highest office, religious discrimination remains an obstacle for Mormon political candidates for president and a vexation for church members.

Two Republican contenders — former governors Mitt Romney of Massachusetts and Jon Huntsman of Utah — have sought to downplay the prejudice in presidential politics.

But a potential problem is hard to ignore: More than 1 in 5 Americans say they would not vote for a Mormon — a figure that has changed only slightly since the question was first asked in 1967, according to Gallup polls.

Dan Peterson, a Mormon and a professor at Brigham Young University in Utah, noted that slim margins decide presidential races in many states, and the anti-LDS factor looms in the background for Romney and Huntsman.

“Whether it will be fatal to their candidacies, I don't know,” he said.

Mormons have run for president before: Sen. Orrin Hatch, R-Utah, fell short in 2000; Sen. Mo Udall, D-Ariz., was unsuccessful in 1976; and Romney's father, George, failed in 1968.

Still, history has a way of setting precedents while seating new presidents. At one time, pundits said a divorcee could not win the nation's highest office, but Ronald Reagan disproved that in 1980, just as Barack Obama broke the color barrier in 2008.

Rep. Jeff Flake, R-Ariz., scion of a prominent LDS family, says Americans who claim they won't vote for a Mormon may relent once they enter polling booths, just as avowed anti-Catholics changed their minds and helped elect John F. Kennedy a half century ago.

“When you have so many other topics to worry about — the economy and jobs — I think people care much less about what church you go to,” Flake said.

In October, Pastor Robert Jeffress of First Baptist Church of Dallas reignited the political controversy by urging Christians not to vote for Romney because of his faith.

“Do we prefer somebody who is truly a believer in Jesus Christ,” Jeffress asked, “or somebody who is a good moral person but he's a part of a cult?”

At church headquarters in Salt Lake City, spokesman Eric Hawkins declined interview requests but said in an email message that the church “doesn't consider honest disagreements on theology to be anti-Mormon. We recognize there are distinct elements of our belief that are different from other Christian faiths. We also believe there is much we have in common and important efforts where we can work together.”

But antagonism doesn't just come from the Christian right: Liberal Democrats are even more likely to reject an LDS candidate. In June, Gallup pollsters reported 27 percent of Democrats would not vote for a Mormon presidential contender, compared with 18 percent of Republicans. The poll's margin of error was plus or minus 4 percentage points.

Pundits note that Mormons are the most right-leaning major religious group in America: A January 2010 Gallup poll indicated that 6 in 10 describe themselves as conservative, especially on social issues, which may explain Democrats' hesitancy.

Yet many Americans know little of Latter-day Saints beyond stereotypes. They see young missionaries on bicycles, wearing white shirts and dark ties, proselytizing door to door. They tell pollsters that, in their minds, Mormons are associated with plural marriage — a practice the church renounced more than a century ago.

Former church members, often the most virulent LDS critics, argue that voters are justified in excluding LDS candidates whose faith might influence public policy decisions.

Richard Packham, the 78-year-old president of the Ex-Mormon Foundation, writes that the church's “ultimate goal” is “to establish the Mormon Kingdom of God in America and to govern the world as God's appointed representatives.”

“I love the Mormons and hate Mormonism,” Packham told The Arizona Republic. “To me, the possibility that the Mormon church might control America is a frightening prospect.”

But Jeff Lindsay, a Mormon scholar who prolifically defends his church on the Internet, says Packham and other critics convey an “awful distortion” of LDS doctrine and practices.

“It's paranoia. It's not based on any example,” Lindsay said. “There is plenty of room for decent people to disagree with us. … But when someone strives to stir up anger toward the church and relies on misinformation or half-truths, then I'm inclined to apply the anti-Mormon label — especially when they do it for a living.”

Although Romney more recently has allowed others to rise in defense, during the 2007 campaign he delivered a pivotal speech to dispel public concerns: “No authorities of my church, or any other church, for that matter, will ever exert influence on presidential decisions,” he declared.

“Their authority is theirs … (and) it ends where the affairs of the nation begin.”

(Dennis Wagner writes for USA Today.)