When a supporter in Council Bluffs, Iowa, nudged Mitt Romney to defend his Mormon faith last week, the Republican frontrunner said he wasn’t planning to. Shouldn’t he be pushing back, she wanted to know, against those who, like his rival Rick Perry’s supporter the Rev. Robert Jeffress, call the Church of Jesus Christ of Latter-day Saints a cult and insist that Romney is not a Christian?

“I don’t think so,’’ the former Massachusetts governor said at a campaign stop in strongly evangelical western Iowa. “I think a great majority of American people want to select the person who is the most capable of getting our country going again with strong values, a strong economy and a strong military; a religious test shouldn’t be applied to people who are running for office,’’ he said to applause. “But,’’ he added, “I am shaped by the Judeo-Christian values which I have and hope that those will hold me in good stead as they have so far.”

It’s a fact of political life that religion has become as much a part of presidential campaigns as it is part of the everyday lives of Americans, and conversations about it on the stump are here to stay. In touting his “strong values” — spelling out that his are of the Judeo-Christian variety, and that they are indeed what shaped him — he’s acknowledging the necessity of explicitly tying his core identity to his faith. But he is also signaling that he’s not planning to get any more specific than he has to, or rush down a road that’s particularly hazardous for candidates whose faith is less well-known, as Romney’s is.

That’s a balance every presidential candidate must now make, on a topic that not so long ago was thought too private — and, yes, too sacred — to be displayed and dissected in public. Romney’s specific predicament, though, is that while American voters overwhelmingly view religious faith as a positive, one in five Republican voters still see Mormonism in a negative light.

This is even more problematic because Romney’s past policy switches mean he needs to prove that he has values he won’t compromise and to speak in detail about where he got them: “I am shaped by the Judeo-Christian values which I have.’’

As a practical matter, Romney couldn’t avoid talking about his faith if he wanted to; “Mormon” was the top one-word description of the candidate in a recent Washington Post-Pew Research Center poll. Nor is there any doubt about his sincerity: The great-great grandson of Mormon pioneers graduated from Brigham Young University, was a missionary in France and while serving as bishop — a lay position in his faith — is known to have bucked up fellow believers both practically and spiritually. Clayton Christensen, a Harvard business professor, recently told the New York Times that during a period when he and his wife were overwhelmed by church and family responsibilities, their lay leader Romney showed up at the door unexpectedly one evening and said, “I was just driving home from work and I had a feeling that I needed to stop by and tell you that God loves you.”

Yet faith-based appeals can easily go wrong, and in keeping with Romney’s low-risk overall strategy, he’s opting against overexposing perhaps the most authentic part of himself to combat the perception that he’s not authentic. When CNN’s Anderson Cooper asked Romney at last week’s primary debate in Las Vegas whether he still wants an apology from Perry, who has said he disagrees with Jeffress but has not repudiated the minister’s remarks, Romney opted for a middle course: “I’ve seen worse,’’ he said mildly. As he very likely will again.

All of his Republican rivals speak more freely about God on the campaign trail, including libertarian Ron Paul, whose campaign Web site includes “faith” as a campaign issue and states, “I have accepted Jesus Christ as my personal Savior, and I endeavor every day to follow Him in all I do and in every position I advocate.” In “This Is Herman Cain!: My Journey to the White House,” the former Godfather’s Pizza CEO credits God with saving him from stage-four cancer five years ago: “God said, ‘Not yet!’ Did it have something to do with the Lord wanting me to survive so that I might help set this great nation of ours on its own path of recovery?”

On the Democratic side, ’04 presidential nominee Sen. John Kerry learned too late that keeping one’s relationship with God off-limits is a luxury that winning candidates can’t afford. In an ’06 address at Pepperdine University, Kerry said: “Despite this New Englander’s past reticence of talking publicly about my faith, I learned that if I didn’t fill in the picture myself, others would draw the caricature for me. I will never let that happen again.”

After Kerry the Catholic lost the Catholic vote, Hillary Rodham Clinton, John Edwards and Barack Obama all talked about their faith in 2008. “It’s a new day,” said Shaun Casey, a religion consultant for Obama. With six in 10 Americans motivated at least to some degree by faith, Casey asked, “why would anyone punt on that?”

And even if Romney is the Republican nominee, Democrats expect conservative third-party Christian groups to recycle the ’08 criticism of Obama’s former pastor, Jeremiah Wright, as part of a full complement of faith-based attacks on the president. Obama’s religion advisers met in Chicago on Friday.

Obama only rarely sounded like a preacher himself after Wright became an issue in ’08. But his opponent, Sen. John McCain, was even more challenged in that regard, and went right back to avoiding God talk after he was criticized for throwing his arm around the Rev. John Hagee, who as it turned out had made remarks offending Jews, Catholics and Muslims. Alan Wolfe, director of Boston College’s Boisi Center for Religion and American Public Life, argues that McCain got the nomination only because anti-Mormon feeling cost Romney the last time around. That bias hasn’t gone away, so “even if he got it this time, he’d have a big turnout problem,’’ Wolfe said.

“For a Mormon political candidate, the strongest selling point’’ to Christian voters, said D. Michael Lindsay, president and professor of sociology at Gordon College in Massachusetts, “is their strength in family life and as good neighbors, active in the PTA and that kind of thing.’’ Hardest to sell, Lindsay said, are theological differences, such as the fact that Mormons do not believe in the Trinity.

Four years ago, Romney lost Iowa to former Baptist pastor Mike Huckabee, who at one point wondered aloud whether Mormons believe that Jesus and the devil are brothers. (Huckabee later apologized, saying that was just something he’d heard.) Yet with the Iowa evangelical vote now divided among his competitors, Romney is back in Iowa. Does the fact that Romney’s audience in Council Bluffs applauded his response mean that voters there are more open this time around? And isn’t there danger, too, in what Perry’s wife, Anita, inferred about him being “brutalized” by his Republican opponents over his faith?

In a response to her remarks in Commentary magazine, Peter Wehner said yes, and he reminded all candidates to be just a shade more careful about claiming that Jesus has endorsed them. After Anita Thigpen Perry tearfully told an audience in South Carolina that she had been called by God to get her husband to run for president, Wehner gently chided her: “All of us, myself included, are tempted to spiritualize what are fairly common (and not terribly spiritual) human ambitions. It’s quite comforting to believe God is calling us to succeed in this world. I don’t pretend to be an expert at sorting through all this. But I do think it’s wise to recall from time to time that humility in understanding the mind of God is a biblical virtue as well.’’

Another potential positive glimmer for Romney on the faith front occurred at the debate in Las Vegas. When audience members at earlier GOP debates cheered for state executions and booed a gay soldier, the behavior did not exactly go unnoticed. But religious intolerance seems to have been shouted down in Nevada, after moderator Cooper asked this question: “With the controversy surrounding Robert Jeffress, is it acceptable to let the issue of a candidate’s faith shape the debate? This is in reference to a Baptist pastor who, at the Values Voter Summit, after introducing Gov. Rick Perry, said that ‘Mitt Romney is not a Christian,’ and that ‘Mormonism is a cult.’ Those were his words.’’ That’s when the booing started — and if anybody wrote about it, I missed it.

Half a century ago, Catholics were regarded much as Mormons are now — with about the same number, 20 percent, indicating that they would be less likely to vote for a Catholic. Then John F. Kennedy gave a speech that made clear he would not be getting his marching orders from the pope, and he won anyway. (Minnesota’s Rep. Michele Bachmann has been urged to make a similar speech during her presidential campaign, distancing herself from her biblical understanding of “submissiveness’’ to her husband, by people who wouldn’t support her under any circumstances.)

The debate audience cheered when former Pennsylvania senator Rick Santorum explained why he finds faith quite relevant for president contenders: “I’m a Catholic. [The] Catholic [Church] has social teachings, teachings as to what’s right and what’s wrong. And those are legitimate things for voters to look at.”

They also applauded Catholic convert Newt Gingrich, whose multiple marriages poll poorly with religious voters, when he said, “I happen to think that none of us should rush in judgment of others in the way in which they approach God.” Then he judged those without faith in God and called it a night: “How can you have judgment if you have no faith?’’ he asked. “And how can I trust you with power if you don’t pray?”

When asked by Cooper, “Will you repudiate those comments” by Jeffress, Perry roamed far and revealed little. (Short answer: No.) Then Romney, not only Perry’s brother in Christ but someone who apparently felt free to lay hands on him, argued with a flash of anger that it wasn’t the casual, smiling slur of the cult comment that he found most offensive. “What I actually found most troubling in what the reverend said in the introduction [of Perry] was he said in choosing our nominee we should inspect his religion. . . . The founders of this country went to great lengths to make sure — and even put it in the Constitution — that we would not choose people who represent us in government based upon their religion. . . . That’s bedrock principle. And it was that principle, Governor, that I wanted you to be able to [repudiate] instead of saying, as you did, ‘Boy, that introduction knocked the ball out of the park.’’ ’

That’s an argument that could play well come next fall. But in the Republican primary, Wolfe and others think the attacks on Romney’s religion have barely begun: “In the old days, the money people would have called Perry and said [of Jeffress], ‘This would kill you in the general,’ but there is no Republican establishment anymore.’’