With one eye on the Scriptures and the other on the White House, contenders for this year's Republican presidential nomination have tussled like barroom brawlers in their effort to capture the vote of America's single largest religious voting bloc: evangelical Protestants.

Organized around conservative positions on a host of social issues, evangelicals make up one-fourth of the adult U.S. population and almost 40 percent of party faithful. They powered Houston-reared U.S. Sen. Ted Cruz's Iowa caucus victory and seemed poised to decide Saturday's GOP primary in South Carolina, where they make up 65 percent of the Republican electorate.

But even as the competition over who has the brightest political halo reaches a crescendo, an unlikely group is waiting in the wings: the "Nones."

Consisting of atheists, agnostics and the religiously unaffiliated, the Nones are experiencing exponential growth and, their supporters believe, may be poised to become a bruising, anti-evangelical political force.

"This is the pivotal time for the nontheist camp to rise up and have their voices heard," said Roy Speckhardt, chief of the American Humanist Association, a group that has advocated and litigated a wide range of church-state separation issues.

Already the Nones, who are challenging evangelicals' numerical strength, are flexing their political muscle.

Center for Freethought Equality, the political action arm of Speckhardt's organization, maintains an Internet report card, rating lawmakers' voting records on humanist issues. Texas congressmen generally rate F's. It lobbies secret nonbelievers in Congress to "come out of the closet" and, in coming months will make public its endorsements for November's election.

In June, American Atheists will sponsor a rally at the Lincoln Memorial, an event expected to attract as many as 30,000 people. And the Secular Coalition for America, representing 18 humanist organizations, is readying the formal launch of a political action Web page, complete with tips for confronting political candidates on humanist issues.

"The way to reach those people," American Atheists director David Silverman said, "is to lead with information on issues they care about - the gender pay gap, gay rights, abortion, death with dignity. When we unite under the separation of church and state platform, everybody who wants equality wins."

'Diverse majority'

In its most recent survey of America's religious landscape, the Pew Research Center found that, propelled by those born after 1981, almost 23 percent of adult Americans identify as atheist, agnostic or "nothing in particular."

That percentage translates to about 56 million individuals and reflects growth far exceeding that of evangelicals. Between surveys in 2007 and 2004, Nones increased by about 20 million; evangelicals by 2 million.

Nones' growth most strongly was felt in the Democratic Party, where 28 percent identified as having no religious affiliation. The group has replaced Catholics as the party's largest "religious" subgroup. Among Republicans, 38 percent identify as evangelicals; 13 percent as Nones.

In Texas, Pew found almost one-third of the state's approximately 20 million adults identifying as evangelicals; almost one-fifth as Nones.

Manny Garcia, deputy executive director of the Texas Democratic Party, said Nones are part of his party's "new diverse majority," a group he said includes whites, Latinos, African-Americans, Asians, believers, nonbelievers and people from across the economic spectrum.

"We're not a single-issue community," he said. "We talk about respecting everybody's view ... A nonbeliever would care about religion in the public space and being enshrined in government policy. But we also care about how we can make families get ahead, education, health care. We're interested in kitchen table issues, the regular issues people are dealing with every night."

The Pew study found that Nones tend to be liberal on issues such as abortion and homosexuality.

Almost three-fourths of atheists, agnostics and religiously unaffiliated say abortion should be legal in all or most cases; only a third of evangelicals agree. Eighty-three percent of nones but only 36 percent of evangelicals favored social acceptance of homosexuals.

Founding values

Larry Decker, executive director of the Secular Coalition for America, cited four principles of the Nones movement: protection of freedom for all individuals, equal protection under the law, knowledge, reason and science and respect for all faiths, including nontheism.

"These are the values unifying our movement. These are the values I believe our country was founded on," Decker said. "We would juxtapose them to the values of the religious right."

In the 2012 presidential election, 70 percent of Nones voted for Barrack Obama; 26 percent for Mitt Romney. Among evangelicals, 79 percent voted for Romney; 20 percent for Obama.

Cruz, the son of a Cuban emigre evangelical preacher, has chided his religious supporters for "ceding the public square" to nonbelievers.

But, despite their burgeoning numbers and the intent of their leaders to weld them into a fighting force, Nones thus far have not proved convincingly potent politically.

In the 2012 presidential election, evangelicals out-voted Nones 2-1.

In Houston, 26-year-old Brian Schrock said his humanist beliefs have fueled political activism.

Schrock, reared in the Church of the Nazarene, said he made a point of voting in the 2012 presidential election and volunteered as a campaign worker in the recent Houston City Council race.

"My social views lean to the candidate who does the most for people," he said. "As a humanist, I'm more open to respecting other people's choices. I definitely support the Supreme Court's same-sex marriage ruling, and I strongly support women's right of choice. On the state level, I'd like to see scientists on the state board of education having a say on how our textbooks are published. My economic views are for what's the fairest for everyone. Empathy is a strong humanist value."

Nones, said Michael De Dora, policy director for the secularist Center for Inquiry, "are a bit more complex than often thought."

The Pew study found more than six in 10 Nones believe in a higher power. "Just that alone," De Dora said, "indicates that we're talking about a community of people who are not necessarily in line theologically."

One commonality, though, he said, "is a strong aversion to very strong, fervent religiosity within politics."

"That's not to say that Nones reject the idea that religion has a role to play in politics," he said. "They're just a little uncomfortable with the super-religious politicians who make their campaign one focused on religion. That makes sense. Even if they're not atheists, they're uncomfortable with organized religion and they look for a broader campaign platform."

'Not political suicide'

Demographically, Pew studies found, Nones and evangelicals have much in common.

Forty-five percent of Nones and 43 percent of evangelicals have no more than a high school diploma; 40 percent of Nones and 34 percent of evangelicals have annual incomes of $30,000 or less. Most Nones are men; most evangelicals, women.

University of Akron professor John Green, a student of the Nones movement, believes atheists, agnostics and religiously unaffiliated may be taking their first steps in building a potent political force.

"Wind back the clock 40 years, and you could say the same thing about the evangelical Protestants," said Green, director of the Ray C. Bliss Institute of Applied Politics. "They were beginning to get interested in politics. It may have looked like a daunting prospect to organize. But they became heavily politicized. I can imagine a similar thing developing with the Nones."

Despite the obstacles, Speckhardt said, Nones are "a group that's finally getting its feet."

In the last mid-term election, the Center for Freethought Equality "raised and spent six figures" to influence political campaigns, he said. "We have such rising numbers that politicians are recognizing our significance."

"A couple dozen" legislators have told Speckhardt's group that they are non-believers. "They were just not ready to go on the record," he said. "We have to show them that this is not political suicide."

In the 2014 Pew survey, 53 percent of respondents said they would be "less than likely" to vote for an atheist. Only 4 percent said they would be "more likely" to vote for a nonbeliever.