(CNN)It's an axiom in American politics, duly repeated every four years: Evangelicals are the country's biggest and most powerful religious voting bloc, especially during the GOP primaries.
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7 types of evangelicals -- and how they'll affect the presidential race
Like many political axioms, though, it papers over a complex reality.
Yes, evangelicals represent a large slice of the electorate, especially in states that vote early in the campaign calendar. In 2012, 57% of people who participated in the Iowa presidential caucuses identified as "born again" or evangelical. This year, evangelicals are again predicted to make up a majority of GOP primary voters in a slew of states that vote by early March.
But evangelicals rarely vote as a bloc, especially in the primaries. They disagree not only on the candidates but also on more basic principles like how active Christians should be in partisan politics.
"The problem is that many secular people think that all evangelicals are alike, when there are multiple streams and theological and generational divides within evangelicalism," said Russell Moore, a leading Southern Baptist.
With the help of experts, we counted seven ways evangelicals approach politics. How well the GOP candidates court each camp could determine their fate in the primaries.
Aging veterans of the culture wars, these evangelicals believe the United States is and should remain a Christian nation, which means they typically flock to conservative Christian presidential candidates. They are hawkish on foreign policy and want politicians who won't give ground on issues like same-sex marriage, abortion and religious liberty.
The old guard's emphasis on political piety and winner-take-all tactics sometimes turns off other evangelicals, particularly millennials.
But their mastery of mailing lists and old-school media like radio ads enables them to mobilize lots of older Christians, especially in states like Iowa and South Carolina. Ted Cruz, who speaks their language, has been endorsed by several of the old guard heavyweights, including Focus on the Family Founder James Dobson.
These evangelicals head megachurches, charities, seminaries and umbrella groups such as the National Association of Evangelicals. They tend to back candidates who, while sharing their core values, stand a solid chance of winning the presidency. Institutional evangelicals rarely endorse politicians but can make their preferences known in other ways. Megachurch pastor Rick Warren and Southern Baptist intellectual R. Albert Mohler, for example, recently joined advisory boards on Marco Rubio's presidential campaign.
Other institutional evangelicals seem to be leaning toward the Florida senator as well, according to polls conducted by the National Association of Evangelicals and WORLD, an evangelical magazine. In a January survey of 82 evangelical "leaders and influencers," 70% favored Rubio.
These evangelicals may not share many theological beliefs, but they all appreciate a good business model. They are evangelists who have built television ministries reaching millions of Americans, and Pentecostal preachers who have turned storefront churches into thriving congregations. Others include Jerry Falwell Jr., who grew the family business, Liberty University, into one of the country's largest Christian colleges.
They appreciate brash personalities who play well on television, and they don't mind a little political incorrectness. Led by his friend, Florida televangelist Paula White, Donald Trump began his evangelical outreach with this group last year. At an appearance at Liberty this month Falwell all but endorsed Trump, telling students the real estate mogul reminded him of his father.
They don't often appear on the radar of mainstream media -- in part because they talk more about Christ than caucuses -- but "arm's length" evangelicals dominate some the most dynamic movements within conservative Christianity. They consider it foolhardy for candidates to use their faith as a footstool to higher office and are reluctant to fuse the sacred sphere of religion with profane politics.
Arm's length pastors include Tim Keller of Redeemer Presbyterian Church in New York, who counsels his congregation to get involved in politics but to be "very critical" of both parties. As he put it: "Don't sell your soul."
John Piper, a former megachurch pastor in Minnesota and one of the most influential evangelical voices, said churches and their ministers should remain apart from political activism. Their job, rather, is to "feed the saints" who perform charity.
Arm's length evangelicals are likely to look askance at a hard sell from presidential candidates like Ted Cruz, who has told evangelicals in Iowa that, "if the body of Christ rises up as one and votes our values, we can turn this country around."
Rubio's approach in this campaign advertisement, in which he explains his faith but doesn't mention political issues, might resonate more strongly with this group.
They've grown up in the shadow of old guard evangelicals, but they're more attuned to the country's religious pluralism than their forebears. "The difference between me and my parents' generation, the culture warriors, is that I actually know people on the other side, and I like them," said Johnnie Moore, an evangelical author who is advising Dr. Ben Carson's campaign.
According to a Pew survey, evangelical millennials are less likely than their elders to identify as politically conservative or oppose same-sex marriage. They are also more supportive of environmental regulations. Most steadfastly oppose abortion, however, with nearly 6 in 10 saying it should be illegal in most cases.
Moore is one of at least three evangelical millennials advising GOP candidates on faith outreach, a sign of their growing political power.
Advantage: Too soon to tell
Yes, they exist! According to Pew's survey, 13% of evangelical Protestants identify as liberal, a number that inches up slightly among younger millennials (17%). Many African-American Protestants also hold evangelical beliefs but rarely vote Republican. For that reason, they are not a force in GOP primaries, though a few have endorsed Trump.
These evangelicals were raised Christian but don't go to church or consider religion that important in their lives. Still, when pollsters ask about their faith, they call themselves evangelical, much like nonreligious Jews still identify as Jewish.
A majority of born again Christians have tended to view Trump favorably, according to Reuters' rolling poll. But his popularity drops significantly among evangelicals who attend church weekly, a key marker of religious commitment.
That may explain why cultural evangelicals don't seem dismayed by Trump's description of Communion as "his little cracker," his inability to name a favorite Bible verse and his recent flubbing of a New Testament reference.
Trump may lose the evangelical vote in Iowa, where church attendance is high, but win their favor in other parts of the country, where faith is more a matter of culture than weekly worship, said Mark Silk, an expert on religion and politics at Trinity College in Connecticut.
"A Southern guy is susceptible to Trump in a way that an Iowa Pentecostal probably isn't."