Former Arkansas governor Mike Huckabee, seen here campaigning in Iowa in early June, is a defender of conservative Christian values. (Scott Olson/Getty Images)

Mike Huckabee — former Fox News personality, Arkansas governor and Baptist preacher — gathered with a modest crowd here in the back of Breadeaux Pizza on his “Main Street American Family” tour and opened the floor to questions.

The very first one set the tone. Jeff Hontz, 49, a Baptist pastor in town, said he has been anxious because he sees “America going down the wrong roads morally.” God decreed unchanging standards in Scripture, Hontz argued, but society keeps changing — and fast.

“I saw a commercial this morning about a transgender show, and everybody was praising it,” he said, prodding the presidential candidate.

Huckabee responded by declaring that the standard of all truth is the Bible. Distorting the laws of nature, he said, is akin to playing the piano without a tuning fork — or baking a cake without the proper measurements of salt, flour and sugar. “You’re going to have a disaster on your hands,” he said.

The exchange illustrates the vexing challenge now facing Republican presidential candidates and the GOP itself: how to get in step with modern America.

A man carries a protest poster outside the Supreme Court in Washington, DC on Friday after its historic decision on gay marriage. (Mladen Antonov/AFP/Getty Images)

Across the cultural landscape, the national consensus is evolving rapidly, epitomized by this year’s convulsions of celebrity, social issues and politics — including the acceptance of Caitlyn Jenner’s gender identity, Pope Francis’s climate-change decree and the widespread shunning of the Confederate flag.

Then came Friday’s landmark Supreme Court decision legalizing same-sex marriage. As rainbow colors bathed the White House and other landmarks in celebration, the entire field of Republican presidential candidates condemned the ruling.

This uneven terrain is now a key battlefield in the 2016 campaign, unnerving red America and fueling intense debate within the Republican Party about how to navigate such changes — or whether to adapt to the mainstream at all.

“Most Republicans look at what’s happening and think we’re watching a new stage of left-wing nuttiness,” said former House speaker Newt Gingrich (R-Ga.). “It’s just surreal.”

The GOP’s activist base wants its leaders to fight loudly for traditional, Christian values and sew together a moral fabric they see as frayed, even shredded. This is especially true here in Iowa, which hosts the first caucuses and where candidates will not easily avoid pressure from the far right. Yet political survival demands evolution with popular opinion.

So far, many contenders are giving the base what it wants.

Republican presidential candidate Donald Trump, seen here in New Hampshire speaking to the media through his SUV window, criticized Mexican immigrants in his announcement speech. (Dominick Reuter/Reuters)

“We’re called upon not to be the thermometers that reflect the temperature in the culture,” Huckabee said in Corydon. “We’re called upon to be thermostats, which can read the temperature and seek to adjust it to where it should be.”

Democrats are hoping for just this approach. They argue — as many Republican Party elites in Washington fear — that if Republicans don’t moderate on issues such as gay rights and immigration and become more tolerant, they will be locked out of the White House. Asked how Democratic front-runner Hillary Rodham Clinton could motivate voters, several top Democratic officials said: The Republicans may do it for her.

“Republicans are going to have to make inner peace about living in a same-sex marriage world,” said Pete Wehner, a former adviser to President George W. Bush. “Our nominee can’t have serrated edges. Like it or not, any effort to create moral or social order will be seen as rigid and judgmental. . . . Grace and winsomeness are the ingredients for success in a world where cultural issues are at the fore.”

‘Get with modern life’

This is a profound shift for a party that a decade earlier won national elections under a banner of social conservatism. In 2004, Bush successfully used his opposition to gay marriage as a wedge issue in his reelection campaign.

“If these topics are the big ones in the general election — rather than the failure of President Obama and Hillary Clinton as his third term, foreign policy, and of course the economy — we can’t win,” said Austin Barbour, a Mississippi-based operative who runs the super PAC supporting former Texas governor Rick Perry. “We need to be sensible, logical and reasonable on the social issues, but also make sure the debate isn’t entirely about them.”

The shifts to the left on social issues may be reinforcing pessimistic beliefs among Republicans about the direction of the country. In a CBS/New York Times poll last month, 88 percent of Republicans said the nation was on the wrong track, compared with 63 percent of Americans as a whole. Meanwhile, 57 percent of Democrats said the country was headed in the right direction.

“When a young voter sees a Republican coming, many of them roll their eyes and wonder why they can’t get with modern life,” said Ari Fleischer, White House press secretary under George W. Bush.

The party’s business wing has been evolving quickly on many social issues, particularly on gay rights. Religious liberty measures in Indiana and Arkansas that many saw as discriminatory against gays drew immediate backlash earlier this year from local chambers of commerce — not to mention corporations such as Wal-Mart, the red-state retail giant — prompting reversals from Republican governors.

“The country is changing, the culture is changing, the demographics are changing and politics is changing,” said former Minnesota governor Tim Pawlenty, now president of the Financial Services Roundtable. “The rhetoric at the congressional level and with some of the candidates tends to be a lagging indicator.”

In far-flung state capitols, legislatures that became more solidly Republican during the past two midterm election sweeps are moving aggressively with social policy designed to combat what conservative lawmakers see as liberal encroachment from Washington. For instance, bills to ban abortions after 20 weeks are moving in several state legislatures.

Politicians are responding to the deep angst conservative activists voice in their communities. At a Huckabee event Wednesday night in Osceola, Iowa, Mary Klein, a 79-year-old school nurse, invoked an urban legend.

“Have you heard about the frogs?” Klein asked. “When you put a bunch of frogs in water and you heat it, they don’t realize the temperature is getting warmer and warmer and warmer. Then it kills them. Our country is getting neutralized, at small degrees at a time, and we won’t realize it until we’re already sucked in and it’s too late.”

‘Kindness of conservatism’

Among the 16 declared or likely Republican presidential candidates, there is general agreement on traditional social policies, such as opposing gay marriage and abortion rights. The differences come in tone, emphasis and countenance.

“We can share our views without sounding like avenging angels,” said Rep. Peter T. King (R-N.Y.). “It’s the self-righteous tone that scares more than the views themselves.”

Major GOP donors, especially those in high finance in New York, have been privately quizzing leading presidential candidates on same-sex marriage. Some have been turned off by Wisconsin Gov. Scott Walker, thinking the son of a Baptist preacher to be too strident in his opposition, and preferring former Florida governor Jeb Bush and Sen. Marco Rubio (Fla.) because they suggest a more ­laissez-faire attitude.

Rep. Tom Cole (R-Okla.), an even-tempered ally of House Speaker John A. Boehner (R-Ohio), recalled: “Ronald Reagan was awfully good at not backing off his position while also never yelling or shouting or pounding the table. Persuasion, persistence and resolve — that was his magic.”

Arthur Brooks, president of the American Enterprise Institute, said that speaking only to the base about issues of God, guns, gays and abortion isn’t enough to win. “Republicans need to recognize this and change the terms of the conversation — or they’ll pay the price for decades,” Brooks said.

One likely candidate trying to soften the party’s language is Ohio Gov. John Kasich, who espouses what he calls “the kindness of conservatism.” A devout Christian, Kasich looks to the activist pope as a model.

In Iowa last week, Kasich advocated a pathway to citizenship for illegal immigrants — a lightning-rod issue in the Republican primary season. When he encountered an undocumented woman and her young son, Kasich said, “They are made in the image of the Lord.”

By contrast, businessman Donald Trump railed against illegal immigrants in his campaign announcement speech. He said the United States had become a “dumping ground” for drug abusers, “rapists” and other criminals from Mexico.

On Thursday night in Iowa, former Pennsylvania senator Rick Santorum gave a fiery speech promising to lead what he called a cultural battle against the “secular left.” He said, “It will be tough to stand against it, but we must.”

Democrats are eager to portray Republicans as the party of Trump, Santorum and Huckabee, as well as retired neurosurgeon Ben Carson, Sen. Ted Cruz (Tex.) and Louisiana Gov. Bobby Jindal — all candidates who proudly resist the shifting social mores.

In a particularly partisan speech Friday night in Northern Virginia, Clinton said Republican candidates “seemed determined to lead us right back into the past” with their responses to the high court’s gay marriage ruling.

“Instead of trying to turn back the clock, they should be joining us in saying loudly and clearly: ‘No to discrimination once and for all,’ ” Clinton said, adding, “A lot of Republicans may talk about having new ideas and fresh faces, but across the board, they’re the party of the past, not the future.”

Housing Secretary Julián Castro, a potential Democratic vice presidential candidate whose ancestors emigrated from Mexico, criticized Trump in a recent interview for “plainly insulting Mexicans and by extension folks who are the descendants of Mexicans.

“He will be in this campaign in many ways the face of the Republican Party, because he has higher name identification than almost all of them,” Castro said.

‘Tolerance only goes so far’

Huckabee, asked during an interview in Iowa how he might modulate his language on social issues, said he does not see any political disadvantage in standing up for his conservative beliefs, as long as voters see them as genuine.

“I think people are deeply interested in issues of morality, character, but it all goes back to trustworthiness and authenticity,” Huckabee said. He added, “The question is: Can I articulate my view, defend it, do it rationally and in a way that’s intellectually honest, without being hateful or spiteful?”

Along Huckabee’s tour in rural Iowa last week, voters dismissed any suggestion that the GOP needed to modernize.

After seeing him campaign Thursday morning at the Dinky Diner in Decatur City, Tracee Knapp, secretary of the Ringgold County Republican Party, concluded that unlike party elites in Washington, “he’s not neutered.”

“I’m just sick of secular things,” she said. “Homosexual issues are on the television all the time. I’ll be honest — we live on a farm. We have to have a bull and a cow to make a baby. We have to have a rooster and a hen. Maybe some Republicans need to come live on a farm.”

The night before in Osceola, Tawny Waske, 49, was celebrating her eighth wedding anniversary with her husband, Tim, at Nana Greer’s Family Table restaurant when Huckabee walked in to shake hands and answer questions. She, too, fretted about cultural changes.

“It’s legalized here for gays [to marry], and we just bite our lips,” Waske said. “As a Christian, we’re taught to love the sinner, not the sin. But tolerance only goes so far.”

Waske brought up ABC’s prime-time special this spring on Jenner’s gender transition.

“Is it him? Her? It? I don’t even know what to call it,” she said. “You know, don’t shove this down my throat.”

Costa reported from Washington. Scott Clement contributed to this report.