Free posters of former U.S. President Ronald Reagan are handed out during the Conservative Political Action Conference in March.Chip Somodevilla AFP/Getty

Quick, name the differences between the tax plans issued this year by Jeb Bush and Marco Rubio.

Stumped? You’re not alone.

The issues that usually drive Republican presidential primaries—taxes, spending, national security—have almost completely fizzled this year. They have been replaced by blazing questions about America’s identity in an era of rapid demographic and cultural change.

Spurred primarily, but not solely, by Donald Trump, the Republican field has spent months debating whether undocumented immigrants from Mexico pose an economic and security threat, whether gays and liberals are waging a “war on Christians” and now, whether Muslims can be trusted as loyal Americans fit for the presidency (not to mention whether President Obama is a Muslim himself).

This succession of searing arguments has transformed the Republican presidential field into a kind of national purification tribunal sequentially debating which groups stand as legitimate members of the American community.

This volatile dynamic has presented Republicans with a stark choice between one set of candidates (including Jeb Bush, John Kasich, Marco Rubio) who essentially argue that the GOP must adapt to cultural and demographic changes, and another group (including Trump, Ben Carson, Ted Cruz, Mike Huckabee and Rick Santorum) who effectively urge Republicans to resist.

The distance between these two camps has elevated the stakes in the primary, for the party and the country. Trump and those echoing him have framed the race as an apocalyptic showdown to protect the nation’s “traditional values,” restore the political primacy of (the implicitly white) “silent majority,” and to “make America great again.”

The candidates and party leaders urging adaptation are warning that the GOP risks exiling itself from the White House by fighting irresistible demographic and social change.

“If you play footsie with this, or if you embrace this view, it is going to be politically suicidal,” says Peter Wehner, a former top White House adviser to George W. Bush. “We are sending in bright neon lights a signal that ‘we don’t like you, we don’t want you…and we consider you the enemy.’ We cannot be in a position of being seen to hate people of different ethnic backgrounds and races and be a winning party.”

After Mitt Romney in 2012 won a larger share of the white vote than Ronald Reagan did in 1980 and still lost to President Obama, those arguing for adaptation initially seized the GOP’s upper hand. That was reflected in the Republican National Committee’s post-election Growth and Opportunity Project, which argued the party could not regain the White House without winning more people of color and Millennial voters.

That impulse crested when Senate Republicans helped to pass a bipartisan immigration reform bill in 2013, but a conservative backlash has steadily suppressed it since.

In this campaign, candidates led by Trump have moved far beyond Romney’s embrace of “self-deportation” of undocumented immigrants with an agenda that includes mass deportation, “a pause” (in Trump’s term) on legal immigration, and ending birthright citizenship. In parallel, other contenders (led by Huckabee, Santorum and Cruz) have insisted that those who object to gay marriage on religious grounds should be exempt from following the Supreme Court decision legalizing it. Now, Carson and Trump have loudly questioned the loyalties of Muslim-Americans. Bush, Kasich and Rubio have sought a middle ground, mostly urging acceptance of a diversifying America—though with more caveats and qualifications (like Bush’s criticism this week of “multiculturalism” and Rubio's renunciation of comprehensive immigration reform) than Democrats typically offer.

The challenge for the Republicans urging adaptation is that, as Trump’s rise has demonstrated, this insular and defensive nationalism strikes a powerful chord in a GOP coalition now centered on older, rural and blue-collar whites. In recent polls a majority of Republicans without a college degree have supported mass deportation and declared that the growing number of immigrants “threatens traditional American values and customs.”

Most Republicans still oppose gay marriage. In a 2013 survey by the nonpartisan Public Religion Research Institute nearly two-thirds of both college and non-college Republicans said they believed “the values of Islam are at odds with American values.” If the choice in the primary is framed as embracing or holding back the emerging Next America, the camp of GOP voters who prefer “resistance to the change is probably larger,” says Daniel Cox, the institute’s research director. And these views are interlocked: PRRI research has found that suspicion of Muslims and hostility to immigrants are closely correlated.

While Americans today divide narrowly on some of these questions (particularly whether Islam is compatible with American values), on most issues public opinion across the entire electorate bends toward tolerance and inclusion—the values that Pope Francis so powerfully celebrated in his Washington appearances this week. That’s especially true among young people, which means the electoral danger for Republicans on these issues of American identity will grow over time—even as Democrats struggle to sell a majority of voters on their approach to economic and foreign policy. “It’s the generational thing that is going to really be a [Republican] problem long-term,” says Cox.

Those electoral risks may help the Republican candidates urging adaptation to erode support for defensive nationalists like Trump even among some voters who mostly share his grievances. But the biggest message from the 2016 race so far may be how large a segment of the GOP coalition is alienated from the kaleidoscope society America is becoming. And that promises turbulence ahead for the party no matter which side prevails in this explosive Republican primary.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.