(CNN) It's uncertain whether President Donald Trump 's proposed border wall will ever separate the US from Mexico. But it's already clear that the wall is reinforcing the fundamental fault line separating blue from red America.

Opinions about the wall have become deeply interwoven with attitudes about the larger changes in culture, demography and gender relations that are reshaping American society. While Trump and congressional Democrats are mostly debating the wall on the grounds of effectiveness and efficiency, polling also suggests that for each party the barrier has become a powerful symbol of whether these underlying changes in American life should be welcomed or resisted.

"Who are we as a country? That's the question on the table," said Robert P. Jones, the founding CEO of the Public Religion Research Institute, a nonpartisan organization that studies public attitudes about religion and culture. "That's a really fundamental question. And it's getting fought out in this symbolic territory over something like a wall, which to both sides can symbolize some of their deepest values and conflicts with the other party."

The wall's symbolic resonance complicates the challenge of reaching a legislative compromise between Trump and congressional Republicans -- who are demanding funding for it as the price of reopening the federal government -- and Democrats, who not only view it as ineffective but are reluctant to validate a keystone of Trump's hardline immigration policies and what many in the party see as a symbol of racism.

During the 1970s and 1980s, political scientists and legal scholars described the battle over abortion rights as "a clash of absolutes" that crystallized the emerging cultural divide between the groups in society that welcomed more permissive attitudes toward sex and more fluid family arrangements and traditionalists led by the emerging religious right movement that mobilized in opposition to them.

In the same way, the wall may be becoming a "clash of absolutes" that crystallizes the key 21st-century cultural divide over the nation's growing ethnic and racial diversity.

"It may be the clearest and most honest debate we've had about the fault lines in the country, but only if you peel it back and recognize it's not just about" border security, said Jones. "With the shutdown and the centrality of the wall you can say at least the real issues are coming straight to the fore."

As I've written before, attitudes toward demographic, cultural and even economic change have become the central dividing line between the Republican and Democratic political coalitions.

Republicans mobilize what I've called a "coalition of restoration" revolving around the groups that express the most unease and hostility about the big changes reshaping America, especially older, blue-collar, evangelical and non-urban whites.

Democrats rely on a competing "coalition of transformation" centered on the mostly urbanized groups that are most comfortable with these changes, particularly young people (millennials and the first post-millennials, who will enter the electorate in 2020), minorities and college-educated and secular white voters, especially women.

In this sharply divided political alignment, the wall looms as a concrete (literally, in earlier versions of Trump's plan) manifestation of deeper views about whether these changes are rejuvenating the country or threatening its traditions.

Views on the wall and race relations correlate

Polling data from the Public Religion Research Institute's annual American Values Survey, conducted last fall, capture how closely attitudes about the wall track views on immigration, race and gender relations.

The Public Religion Research Institute poll is especially revealing because it asked opinions about the wall as part of a much broader survey examining Americans' attitudes toward a wide range of cultural and demographic changes. It found that wall supporters and opponents express virtually mirror-image views on those broader shifts, according to previously unpublished results from the poll provided to CNN.

It may be least surprising that views about the wall track with opinions about immigration's impact on American society. Wall supporters express vastly more hostile views than wall opponents about the impact not only of undocumented but also legal immigration.

In the Public Religion Research Institute survey, three-fourths of adults who support the wall say immigrants burden local communities because they use too many public services; two-thirds of wall opponents say immigrants are not an undue burden.

Two-thirds of wall supporters say it bothers them when they come into contact with immigrants who don't speak English well; three-fourths of wall opponents said it does not bother them.

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Likewise, two-thirds of wall supporters say the growing number of immigrants "threatens traditional American customs and values," while four-fifths of opponents say the change instead "strengthens American society."

Over eight-in-10 wall supporters back a temporary ban on immigration from some Muslim countries, while three-fourths of wall opponents oppose a ban. And while nearly seven-in-10 wall opponents reject legislation to reduce the level of legal immigration, over eight-in-10 wall supporters want the US to accept fewer legal immigrants.

But views about the wall also closely correlate with attitudes about race relations.

In the Public Religion Research Institute survey, three-fourths of wall supporters said recent police killings of African-Americans were "isolated incidents" rather than "part of a broader pattern of how police treat" blacks. However, almost three-fourths of wall opponents saw a broader pattern.

Almost exactly three-fourths of wall supporters rejected the idea that "generations of slavery and discrimination have created conditions that make it difficult for blacks to work their way out of the lower class." Nearly two-thirds of wall opponents agreed with that statement.

Perhaps most dramatically, almost two-thirds of wall supporters said discrimination against whites is now as big a problem as discrimination against minorities. Three-fourths of wall opponents rejected that view.

The gulf between wall supporters and opponents extends even to views about changing relations between men and women. Nearly two-thirds of wall opponents say the feminist movement accurately reflects the views of most women. Nearly two-thirds of wall supporters say it does not.

Just over three-fifths of wall opponents say the #metoo movement has helped "address sexual harassment and assault in the workplace"; less than half as many wall opponents agree. One in three wall supporters say the movement has "led to the unfair treatment of men"; only one-in-11 wall opponents agree.

On the broadest measure of gender relations, just 25% of wall opponents believe discrimination against men is now as great a problem as discrimination against women, while 74% reject that view. By a 54% to 45% majority, wall supporters say men do face as much discrimination as women.

On the most sweeping measures, wall opponents express enormous anxiety about the direction of social change in the country, while supporters are much more optimistic.

When reminded that the Census Bureau projects that racial minorities will compose a majority of the nation's population by around 2045, fully 82% of wall opponents said the effect of the change will be mostly positive, while only 16% believed it will be negative. Wall supporters took a very different view: 58% expected the changes to trigger mostly negative impacts, while just 38% expected positive change.

Three-fourths of wall supporters agreed that the "American way of life needs to be protected from foreign influence." Almost two-thirds of wall opponents disagreed.

'The Breitbart version'

Perhaps most tellingly, the two sides produced almost exactly inverse responses on a summary question that collects attitudes on all the changes remaking American life. Fully 59% of wall supporters agreed that "things have changed so much that I often feel like a stranger in my own country." An identical 59% of wall opponents disagreed with that sentiment.

The veteran Democratic pollster Stanley B. Greenberg has long argued that Democrats must respond more to concerns among voters, particularly working-class whites, about the economic and security implications of immigration. But Greenberg says Trump has made it easy for Democrats to coalesce in opposition to his wall by so clearly making it a symbol for hostility to growing diversity overall.

"President Trump made the wall the symbol for America being threatened by invading dark people, hiding Islamic terrorists," Greenberg in an email. "Democrats are right to call it out and not fund it."

Greenberg says the Republicans now marching in lockstep behind Trump in the partial government shutdown over the wall face the risk of being identified with the same insular racial attitudes that repelled many suburban voters from the party in November's elections.

No poll during the shutdown -- or for that matter earlier in Trump's presidency -- has found that a majority of Americans support the wall. And other surveys have found that the share of Americans who view immigration favorably has been rising as Trump has not only raised alarms against undocumented immigrants, but also proposed the largest reductions in legal immigration since the 1920s.

With the shutdown over the wall Trump is offering "the Breitbart version of America's challenges and it was forcibly rejected at midterms," Greenberg wrote.

Still Greenberg believes Democrats must make clear that they also view border security as a priority -- and are not just focused on finding a pathway to citizenship for undocumented immigrants, which he maintains is the message Hillary Clinton projected in 2016.

In an ordinary legislative confrontation, both parties' desire to express concern about border security would usually lead them toward a compromise that incorporated priorities of each side (including possibly protections for immigrant populations such as the young people brought to the country illegally by their parents).

The problem is that in this "clash of absolutes," the wall has acquired such symbolic power for each side that it would require enormous dexterity to craft a solution that allows both sides to insist they have held firm.

In particular, as Jones notes, for Trump the wall has become the physical embodiment of his core promise: to make America great again by reversing the economic, cultural and demographic changes that his supporters believe have marginalized them.

"The way that Trump has talked about himself, even in the campaign, is as a kind of wall," Jones said. "All this talk that, 'I'm the only one who can stop the changes you don't like,' 'I am the only thing standing between you and hordes of people on the border,' 'I am the only one who can roll back the clock. ... I am the thing standing between you and chaos.' That's what walls symbolize.

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"The wall is kind of perfect for Trump because for a long time he has characterized himself as a kind of wall against these cultural and demographic changes that conservative whites and especially white Christians really worry about."

The political problem for Republicans is that on almost every major question, Trump's promise to resist demographic and cultural change leaves them playing to a minority of the public -- as polls on the wall have made clear.

The political problem for Democrats is that the structure of the Electoral College and especially the two-senators-per-state rule magnify the political influence of the voters in that minority, particularly non-college whites.

The problem for both sides is that finding compromise on any issue relating to race and inclusion is growing much more problematic while the two parties hold views about social change as diametrically opposed as those recorded in the Public Religion Research Institute survey.

With attitudes toward the wall closely tracking views on all the big cultural and demographic changes reshaping America, the shutdown debate captures the difficulty of reaching any consensus about the nation's evolving identity between the coalitions of transformation and restoration.

Whether this impasse is resolved with or without a new barrier along the border, the struggle has offered a searing reminder that the internal walls between what America has been and what it is becoming are only growing higher and more impassable.