At a dinner with Iowa religious leaders recently, Marco Rubio opened up about his relationship with Jesus. He described what he had learned from studying the Bible, especially the Apostle Peter, and spoke of the importance of self-sacrifice as illustrated in the story of Abraham.
But after he spoke, a pastor from Des Moines pressed him about a more earthbound issue that is troubling some conservative evangelical voters: Mr. Rubio’s support from the New York financier Paul Singer, a high-profile contributor to efforts to legalize same-sex marriage.
“These guys give some money, and they expect something in return,” the pastor, Mike Demastus, said later in an interview. “If Rubio is in the Oval Office, Mike Demastus could not call and get through. But Paul Singer could. That’s what I know.”
Mr. Singer, a billionaire who has poured millions of dollars into gay rights causes, announced this fall that he would devote his considerable fund-raising muscle to electing Mr. Rubio president, elevating the Florida senator’s candidacy in the influential network of hedge fund executives that Mr. Singer inhabits.
But the doubts religious conservatives express over that endorsement capture the difficulty Mr. Rubio faces as he seeks to stitch together a disparate coalition of powerful establishment figures like Mr. Singer and the faith-driven voters who are a critical part of the Republican base.
Even Mr. Rubio’s religious background is a bit of a mystery to evangelical voters in Iowa. The senator was initially raised Roman Catholic, converted to Mormonism, returned to Catholicism and now attends both a Catholic church and a Southern Baptist-affiliated church where his wife is a member.
Mr. Rubio has been lagging among religious conservatives and has begun emphasizing his Christianity on the campaign trail, in ways overt and subtle.
The latest Quinnipiac poll of likely Republican caucusgoers in Iowa found him at 8 percent among people who said they were white evangelical or born-again Christians, far behind Senator Ted Cruz of Texas (27 percent), Ben Carson (24 percent) and Donald J. Trump (20 percent). Pastor Demastus is backing Mr. Cruz. Evangelicals are expected to play an outsize role in several early contests, particularly in South Carolina, which holds the nation’s second primary, and in the first multistate primaries on March 1, when many Southern states will vote.
Mr. Rubio’s more open discussion about his religion is cracking a window into a part of his life he does not often discuss. Sometimes he goes on at length, as at the dinner in Des Moines, demonstrating a fluency with Scripture that surprises his audience. When he spoke of the Apostle Peter that night, he offered this lesson: “Once he was infused in the Spirit, that impulsiveness was used as a tool for God’s plan.”
He allowed only one journalist inside to film him: the Christian Broadcasting Network’s chief political correspondent.
Many of his other gestures are small, but do not go unnoticed by evangelical voters. There was the time last month when he said on “Good Morning America” that he experiences financial strain like any other family, in part because “I send my kids to private Christian schools.”
He speaks often of the importance of religious liberty as not only a right to believe but also “the right to exercise your faith in every aspect of your life,” a nod to people who are worried they will be forced to accept same-sex marriages.
The Rev. Jamie Johnson, from Story City, Iowa, who helped organize the dinner, described a largely unquantifiable factor that could benefit Mr. Rubio over more abrasive candidates like Mr. Cruz and Mr. Trump. He called it Iowa’s 11th Commandment: “Thou Shalt Be Nice.”
“It’s not enough to be a conservative policy advocate,” Pastor Johnson said. “You have to be likable.”
In 2012, 57 percent of Republican caucus voters in Iowa described themselves as evangelical or born again. And many of them now say that Mr. Rubio is getting a late start with them.
After hearing Mr. Rubio speak in Des Moines, one prominent Christian leader, David Lane, said he could not understand why the senator had not given a speech like that sooner. “He’s very, very conversant in the word,” he said. “This guy is not just a casual Christmas- and Easter-only churchgoer.”
But, as Mr. Lane put it, “a lot of people are already gone.”
Mr. Rubio has never seemed comfortable with the public testimonials of faith that are almost ubiquitous in states with large Christian conservative populations like Iowa.
Many religious voters find his personal faith something of a curiosity.
Mr. Rubio has described a lifelong multidenominational journey. The son of Cuban immigrants and born in Miami, he was raised initially as a Roman Catholic. But after his family moved to Las Vegas when he was 8, his Mormon relatives there persuaded his mother to baptize the family into the Church of Jesus Christ of Latter-day Saints, where they remained active for three years.
At the pastors’ dinner in Des Moines, Mr. Rubio professed to have a nagging curiosity about Catholic theology that started as an adolescent, saying that drove him to help persuade the family to rejoin the church. “I didn’t learn about the Catholic Church until I went to a non-Catholic church,” he explained.
Today, he and his wife sometimes attend a Southern Baptist-affiliated church in Miami called Christ Fellowship, though he said he considered himself “theologically and doctrinally aligned” with the Roman Catholic Church. He said he listened to podcasts by the Christ Fellowship’s lead teaching pastor, Rick Blackwood, whom he has called “an incredible teacher of the written word.”
Same-sex marriage, and Mr. Singer’s prominent role in the issue, is particularly sensitive for Mr. Rubio among conservatives. About 70 percent of white evangelical Protestants oppose same-sex marriage, while 39 percent of all Americans do, according to the Pew Research Center.
Mr. Singer is perhaps the most prominent Republican donor calling for the party to embrace same-sex marriage. Mr. Singer, who has a gay son, founded American Unity PAC, which provides financial support to Republican-elected officials who support same-sex marriage. A related policy group backed by Mr. Singer, American Unity Fund, is seeking to rewrite the Republican Party platform to embrace gay rights.
His relationship with Mr. Rubio dates from 2010, when he backed his candidacy for Senate. But Mr. Singer’s declaration of support for Mr. Rubio’s presidential campaign — and his determination to build a network of donors for him — has brought new attention to the relationship, touching off conservative criticism.
The website Breitbart.com greeted the news of his endorsement last month with the headline “Kiss of Death: Billionaire Who Funded Same-Sex Marriage Endorses Rubio.” That reflected a widespread skepticism in the conservative press. A headline in Newsmax, the right-of-center news site, declared, “Rubio’s New Billionaire Backer Has Gay Marriage Agenda.”
Some supporters of Mr. Rubio see the fingerprints of the Cruz campaign in efforts to taint Mr. Rubio with his association with Mr. Singer.
Mr. Rubio is now accustomed to questions about Mr. Singer coming up from skeptical conservatives, and repeats his position that he has never supported same-sex marriage. His donors buy into his agenda, not the other way around, Mr. Rubio has said.
His recent appointment of a director of faith outreach for his campaign seemed to underscore his message to evangelicals concerned about the issue. Mr. Rubio hired Eric Teetsel, a 31-year-old activist who condemns homosexuality and once wrote of his experience supporting a friend who was trying to repress his same-sex attractions.
Mr. Singer, who seldom talks to the news media about his political agenda, declined to be interviewed for this article. Mr. Teetsel has not been as shy. A frequent blogger on social issues, he declared that the Supreme Court decision last June that legalized same-sex marriage would result in the spread of sin.
“This is regrettable because sin, of course, leads to suffering,” Mr. Teetsel wrote. “As our L.G.B.T. neighbors continue to experience the ravages of their sin, will anyone be there to explain to them its cause?”