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.