This presidential primary season, God is in the details.

For Republican candidate Mitt Romney, that means his political future may hinge on whether he can convince the nation's conservative evangelical Christians that even though he may pray to a God with a different form than theirs, diverse religious expression is vital to America's freedom.

Romney's views on the nature of God and Jesus, as well as his beliefs about whether the Bible is infallible, are central to the distrust many evangelicals feel about Romney as a potential president, according to interviews with evangelicals and others.

The bottom line: Romney may say that Mormons are Christians, but many evangelicals aren't buying it.

Romney supporters see the focus on his faith as something of a "religious test" for a secular office, a criterion that is forbidden in the Constitution. Evangelical opponents argue that Romney's theological beliefs have a bearing on how he would run the country.

Romney tried to address those concerns during Thursday's speech in Texas, where he not only assured voters that Salt Lake City would not influence his decisionmaking but also that American values "belong to the great moral inheritance we hold in common. They're the firm ground on which Americans of different faiths meet and stand as a nation, united," he said.

But theology may trump those "moral values" for some conservative Christians.

Romney knows he can't win the GOP nomination without a large base of support from some 70 million evangelicals, the most conservative of whom say they will never vote for a Mormon. Challenger Mike Huckabee, a former Baptist minister and former governor of Arkansas, figures that Romney can't win in heavily evangelical states, including pivotal Iowa, if he is forced to detail the specifics of his faith that are untenable to the majority of these voters.

In Thursday's "Faith in America" address, Romney shied away from giving those details, choosing instead to focus on the values his religion shares with other religious people. The closest he came to expressing his theology was the statement, "I believe Jesus Christ is the Son of God and the Savior of mankind."

That profession of faith may not satisfy conservative evangelicals, says James Wakefield, a professor at Salt Lake Theological Seminary. "The most conservative folks are going to fault him for basically using common terms that allow him to mask himself as the same as other Christians."

Although these nuances will baffle many voters, who can't understand why a candidate's beliefs about the Trinity or the Bible should matter at all, theological differences are key for evangelicals, according to researchers at Vanderbilt and Claremont universities. Their poll, released Wednesday, found that for conservative evangelicals surveyed, Mormons rank nearly as objectionable as atheists.

"When we say Romney is a Christian and Mormons say they are Christian," Southern evangelical respondents "become very defensive," reported Brett Benson, assistant professor of political science at Vanderbilt, who is a member of The Church of Jesus Christ of Latter-day Saints.

The Christian belief in the Trinity has been an issue in three elections — in 1800, 1908 and today — according to Forrest Church, a Unitarian minister in Manhattan and author of "So Help Me God: The Founding Fathers and the First Great Battle Over Church and State."

"The question is: 'Is Jesus God?' That's the kicker of the Trinity," Church explains. "Do you believe in the full divinity of Jesus and that only through Jesus can you be saved? If your whole faith is based on that, the moment you have a unitarian — whether you be a Universalist Unitarian, a Muslim unitarian, a Mormon unitarian — you have lowered that status of Jesus from his full divinity."

"These things become incredibly emotional," because the implication is that a nation without a leader who believes that Jesus is God will not be saved. "People argued when Jefferson was elected that Armageddon would come here and now."

If you go back to the 3rd and 4th centuries post-Christ, says the Rev. Wade Halva of Cottonwood Presbyterian, "the Trinity was the litmus test for orthodoxy." Today, he says, "it's kind of a secret handshake," a way of saying "this is what it means to be a 'real Christian."' But it's also more than just a code. Evangelicals believe that "if we don't agree about who God is, we won't agree about what God calls us to do," he says.

Whole books have been written to explain the Trinity. Here's how Franklin Evans used to explain the Trinitarian vs. unitarian view to his Methodist confirmation classes: "If God, Jesus and the Holy Spirit were coming to dinner, how many places would you set?" For people who believe in the Trinity, the answer would be "one." The Trinitarian view is that God, Jesus and the Holy Spirit are one divine being composed of three persons, explains the Rev. Pat Edwards of Bountiful's Grace Baptist Church.

Mormons, on the other hand, believe that God the Father, and his literal son, Jesus Christ, are separate beings with physical bodies of flesh and bone like those of men, only perfected. Together with the Holy Ghost, "a personage of spirit" according to LDS scripture, the three members of the Godhead are "one in purpose" but not in body.

The Trinity is chief among historic Christian doctrines that Mormons believe LDS Church founder Joseph Smith dispelled during what is known as "the First Vision." Smith said God and Jesus Christ appeared and spoke to him as separate beings in the spring of 1820, in answer to his prayer seeking guidance about which sect of Christianity was right so he could join.

"I was answered that I must join none of them, for they were all wrong ... that all their creeds were an abomination in his sight," Smith later wrote. Mormons believe those "creeds" were formulated and voted upon by clergy in the third and fourth centuries seeking to codify the nature of God, Christ and the Holy Spirit, and were departures from the "fullness" of Christ's original teachings.

"To the extent that creeds divide people, categorize people, exclude people and even lead others to persecute them, one can appreciate why they would be viewed as undesirable," wrote Robert Millet, former dean of religious education at Brigham Young University, in his recent book, "The Vision of Mormonism."

"To the extent that they become a badge of belonging, the identifying mark by which a 'true Christian' is known, the only way by which one can understand what the Scriptures really mean about God and Christ — then to that extent the Christian circle is drawn smaller and smaller, and that grace of God that makes salvation to all humankind is frustrated."

Mormons don't shy away from pronouncing that Jesus Christ is their Savior and the head of their church, emphasizing that the faith's name — The Church of Jesus Christ of Latter-day Saints — denotes the centrality of his role in their faith, which makes them Christians. But evangelical leaders reject that assertion, saying it has become a semantics game.

This is how Grace Baptist Church's Rev. Edwards sees it: "We use the same name for Jesus, and we use the same story, but when we describe him we understand he's not the same person as you do. The same for God. Your Jesus was born of the Father, mine has existed eternally. My Jesus is God."

His God, says Edwards, is unchanging, has eternally existed and "chose a human form for 33 years to take on our sins."

Edwards, though, thinks conservative Christians have become "overly political" and doesn't think America needs to become "a quote Christian nation led by a Christian leader. Not that we're against it, but we don't feel we need it."

For some evangelicals, says Salt Lake Theological Seminary's Wakefield, "the most worrisome thing is the LDS doctrine of 'exaltation.' ... It brings lots of questions of who is aspiring to what kind of power."

For Latter-day Saints, "exaltation" means righteous men and women "who attain the highest level in the celestial kingdom (heaven) become gods, receive exaltation and are joint heirs with Christ of all that (God) the Father has," according to the Encyclopedia of Mormonism.

The doctrine was taught by the fifth president of the LDS Church, Lorenzo Snow, who said, "As man now is, God once was. As God now is, man may be."

According to the Encyclopedia of Mormonism, that is a similar view of salvation as the early Christian "theopoiesis," in the second and third centuries, which means literally, "being made God."

"Due to its incongruity with the doctrine of God in Western Christianity, deification fell out of favor as the preferred way of describing salvation," the reference work says.

"I don't think it's at all necessary to say that any LDS person is going to be more Machiavellian or grasping after power than anyone else," says Salt Lake Theological Seminary's Wakefield, himself an evangelical. "I want to be fair to lots of humble people in Utah. But in the most conservative of evangelicals' minds, one of the most distinctive parts of (Mormon) theology makes them go 'Wow' and wonder if this is more of a power grab."

But should any of this really matter to the presidential race?

Humility, wisdom and a strong commitment to justice are what matter in a candidate, not "narrow beliefs of this, that or the other," says The Right Rev. Carolyn Tanner Irish, bishop of the Episcopal Diocese of Utah. "I'd rather have someone who cares about the poor than somebody who recites the Nicene Creed every day."

A doctrine like the Trinity should have no bearing on whether a person would make a good president, says the Rev. Steven Goodier of Christ United Methodist Church in Salt Lake City. On the other hand, he says "theology does matter, in so far as it informs who a person is." If, for example, a person's theology is that the world is going to end in the near future, he's not going to care about the environment, Goodier says.

"He's not running to be theologian-in-chief," argues Unitarian minister and historian Church, echoing Romney's oft-repeated assertion that the country is not choosing a "pastor-in-chief."

For their part, most Mormons can't understand why there is any question about whether they are Christian, and what their values are.

"I was taught in my home to honor God and love my neighbor," Romney said Thursday. "I saw my father march with Martin Luther King. I saw my parents provide compassionate care to others, in personal ways to people nearby, and in just as consequential ways in leading national volunteer movements."

Quoting Christ from the Bible, he said, "My faith is grounded on these truths. You can witness them in Ann and my marriage and in our family ... our aspirations, our values, are the self-same as those from the other faiths that stand upon this common (moral) foundation."

The first time religion was an issue in a presidential campaign, Church says, was in 1800, when Thomas Jefferson ran against incumbent John Adams. Jefferson was considered an "infidel" because he questioned the creation narrative in Genesis, didn't believe in the Trinity and defended church-state separation. If Jefferson wins, predicted the editor of the "Connecticut Current," "murder, robbery, rape, adultery, and incest will be openly taught and practiced, the air will be rent with the cries of distress, the soil will be soaked with blood, the nation black with crimes."

Religion was again an issue in 1908, when candidate William Howard Taft was criticized because he was a Unitarian. Although there had been three other Unitarian presidents (both Adamses and Millard Fillmore), by this time the Unitarians — who, as their name spells out, don't believe in the Trinity — had become an "outsider church" and thus suspect, Church says.

At that point, outgoing president Theodore Roosevelt wrote a letter to the country arguing that a person's religious beliefs have no place in electoral politics. "His letter served the same purpose as Kennedy's speech in Houston served: it neutralized the issue," Church says. Taft won in a landslide.