Florida Senator Marco Rubio speaks to supporters during a rally at a restaurant on August 5, 2015 in Cleveland, Ohio.National Journal

Sen. Marco Rubio of Florida was crisp, compelling, and dynamic at the first Republican presidential debate last week. In an extensive follow-up interview on Meet the Press this Sunday, he was thoughtful and energetic. Each occasion highlighted the potential of Rubio, a 44-year-old Cuban-American, to offer a fresh, forward-leaning image in 2016 to a Republican Party now inordinately reliant on the votes of older whites.

"For our party," Rubio insisted on Meet the Press, "it's incredibly important that we be seen as a movement about the future."

And yet, in those same forums, Rubio underscored his renunciation of the comprehensive immigration-reform legislation he helped steer through the Senate in 2013, and embraced a position on abortion more conservative than any Republican presidential nominee since Ronald Reagan.

In that way, Rubio crystallized the most complex electoral challenge facing Republicans in 2016: navigating the towering waves of demographic and cultural change transforming American life.

With opinion divided over President Obama's impact on both the nation's economy and its security, the Democrats' most potent weapon in the 2016 election remains the sense that they are more connected than the GOP to the nation's evolving cultural and demographic dynamics. As last week's GOP first- and second-tier debates demonstrated, the party's presidential field is struggling to steer between a country that is rapidly reconfiguring itself, and a conservative base resistant to many of those changes.

Polling by the nonpartisan Public Religion Research Institute underscores the depth of disaffection among many Republicans toward the demographic and cultural forces recasting America. While 63 percent of Democrats said in a recent institute poll that "the growing number of newcomers from other countries" strengthens American society, just 36 percent of Republicans agreed. On a broader institute question last year, 62 percent of Republicans said that since the 1950s the "American culture and way of life" has changed mostly for the worse. Virtually the same share of Democrats (59 percent) said society since then has changed mostly for the better.

"Whether gender roles, the decline of religion, immigration, multiculturalism — there is this visceral discomfort among Republicans and conservatives that America is changing in ways that 'I don't like,'" said Daniel Cox, the religion institute's research director.

In this campaign, Donald Trump's fulminations against undocumented immigrants have most viscerally concentrated that broader anxiety. But, like steam venting through cracks in the Earth, that unease resurfaced in other ways during last week's GOP debates. Viewers heard multiple candidates heatedly denounce the Supreme Court decision legalizing gay marriage, promise a hard line against any legal status for undocumented immigrants, propose to limit legal immigration, pledge to defund Planned Parenthood, and underscore their opposition to legalized abortion.

The most dramatic moment in the debate that did not involve Trump came when Rubio forcefully rejected the suggestion from questioner Megyn Kelly that he would not ban abortion in cases of rape or incest. Rubio then reiterated his opposition to exempting rape and incest from any abortion ban in a round of post-debate interviews. In his Meet the Press interview, the senator would not even unequivocally commit to supporting legal abortion in a pregnancy that endangered the life of the mother.

"Whether gender roles, the decline of religion, immigration, multiculturalism — there is this visceral discomfort among Republicans and conservatives that America is changing in ways that I don't like." — Daniel Cox, Public Religion Research Institute

With his assured debate performance, Rubio showed why many Republicans believe he offers the most compelling contrast to Hillary Clinton, the likely Democratic nominee. Yet the position he clarified on abortion could prove a heavy load in a general election. Polls show three-fourths of Americans (and even 71 percent of Republicans) oppose banning abortion in cases of rape. From George H.W. Bush in 1988 through Mitt Romney in 2012, every Republican presidential nominee has proposed to ban abortion, but also supported exceptions for rape, incest, and saving the life of the mother. The last GOP candidate to advance a position as hard-line as Rubio's was Ronald Reagan in 1980 and 1984.

That's an appropriate bookend for Rubio's declaration.

The GOP's underlying political debate this year is whether the party must try to broaden its reach to younger voters and voters of color with new policies, or if it can still win without recalibrating its agenda by mobilizing a Reagan-like coalition that relies almost entirely on culturally conservative whites. At the debate, both Ohio Gov. John Kasich (on gay marriage) and former Florida Gov. Jeb Bush (on immigration) made the case for new thinking by striking a markedly more inclusive tone than their rivals.

Wisconsin Gov. Scott Walker and the blustery Trump each embody the latter proposition. Rubio has bounced between the alternatives: He has offered some new thinking (notably on college affordability) but on many issues has reverted to familiar conservative orthodoxy, especially after the Right erupted against his immigration-reform legislation.

Republicans can't simply ignore the cultural unease felt by many evangelical Christians and other conservatives central to their electoral coalition. But they are still seeking a formula to reconcile those anxieties with the realities of a swiftly changing society. Rubio, arguably their most forward-looking candidate, inadvertently demonstrated that dilemma by reviving an uncompromising position on abortion, one the party last tried to sell in a presidential election more than three decades ago to a country very different than it is today.

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