(CNN) Few questions may shape the result of the 2020 election more than whether Democrats can exploit the religious gap in attitudes toward President Donald Trump that has emerged among his core constituency of working-class white voters.

While polls generally show Trump retaining strong support overall among blue-collar whites, more detailed results in several recent surveys reveal a critical distinction: Trump faces much more resistance among working-class whites who are not evangelical Christians than among those who are. If Democrats can advance through that opening, it could prove crucial in 2020, because evangelicals compose a much smaller share of the white working-class population in the pivotal Rust Belt battleground states, such as Michigan and Wisconsin, than they do in the South.

The divergence over Trump between working-class whites who are and are not evangelicals "is one of the most important political gaps we have," says Robert P. Jones, founder and CEO of the Public Religion Research Institute, a nonpartisan organization that studies the role of religion in politics.

The widening polarization of the electorate during Trump's tumultuous presidency is magnifying the potential impact of that gap in 2020. The working-class white voters who are not evangelical Christians, especially the women in that group, loom as a potentially decisive swing block between the evangelicals who have rallied around Trump and the non-evangelical college-educated whites who have recoiled from him.

On a wide array of cultural and political questions, these non-evangelical blue-collar whites express views that place them between those two antithetical voting blocks. On balance, they lean toward culturally conservative positions, but not nearly as fervently as the evangelical Christians do. And while they express clear concerns about Trump's conduct during his presidency, they aren't nearly as alienated from him as the non-evangelical whites with advanced education.

On every front, these voters look closely divided. "They are cross-pressured," says Jones.

Voters with most conservative views

In the 2018 election, these three groups were roughly similar in size, according to results from the exit polls conducted by Edison Research for the National Election Pool, a consortium of media organizations including CNN. White evangelicals at all education levels and college-educated whites who are not evangelicals each cast about 1 in 4 votes. The non-college whites who are not evangelicals represented a little more than one-fifth of voters, with racial minorities making up the remainder.

The Public Religion Research Institute's annual American Values Survey , released last month, provides a precise snapshot of these differences. At my request, for several central questions the institute examined the results among these key groups of white voters. First, they divided whites into those with and without four-year college degrees. Then they divided those groups into those who are and are not evangelical Christians. Finally, they split the groups a third time, by gender. (College-educated white evangelicals were too small a group to divide again by gender, so they reported the results for men and women combined; to keep the results comparable, they also reported the results for the college-educated non-evangelicals among both genders.)

The results showed that white evangelicals without college degrees consistently take a more conservative stance on social and economic issues than any other segment of voters. The men and women in that group differed little in their staunchly conservative perspective, particularly on issues that touch on racial anxieties.

For instance, 75% of non-college white evangelical men and 65% of the women agreed that discrimination against whites is now as big a problem in America as discrimination against minorities; three-fourths of the men and two-thirds of the women also agreed with the harshly worded statement that "Immigrants are invading our country and replacing our cultural and ethnic background." Four-fifths of the men and two-thirds of the women agreed it is "necessary to believe in God to be moral and have good values." Three-fourths of the men and two-thirds of the women agreed that the "Democratic Party has been taken over by socialists."

Differences among white evangelicals

An even greater share of college-educated white evangelicals (four-fifths of them) said they believed socialists had taken over the Democratic Party. But on cultural issues, those white-collar evangelicals were considerably less militant than their working-class counterparts. Only a little more than half of the college evangelicals agreed that immigrants are "invading" the country or that whites face as much discrimination as blacks; a slight majority of them even rejected the idea that it was "necessary" to believe in God to be moral.

Jones says the contrast on these responses illuminates a larger point: that the college-educated evangelicals are somewhat less likely to feel a sense of "siege" in a changing America than their working-class counterparts do. "They are less apocalyptic and less apoplectic than non-college evangelicals," he says. Still, the non-college white evangelicals set much more of the tone for the group overall because they represent about 70% of the evangelical population, studies by Public Religion Research Institute and other groups have found.

The educational differences among evangelicals extend even to one key assessment of Trump: Just over half of the college-educated evangelicals, compared with only about one-fourth of those without degrees, said in the religion research institute's survey that they believe he has damaged the dignity of the presidency.

But that skepticism extends only so far: Even three-fourths of the college-educated white evangelicals in the institute's survey said they approve of Trump's performance in office, a result comparable to his support among those without degrees. And just 16% of those college evangelicals support Trump's impeachment and removal from office, compared with 7% of non-college evangelical men and 23% percent of the women. Across all educational levels, evangelical Christians "are still a solid Trump constituency," says Jones. "They really haven't walked away."

Non-evangelical whites and Trump

At the other end of the spectrum among white voters, Trump faces huge skepticism among college-educated whites who are not evangelicals. These voters, often clustered in suburbs around major metropolitan areas, had been trending toward the Democratic Party since the early 1990s, as cultural issues such as abortion, gun control and gay rights increasingly have defined political debate. That movement has been turbocharged as Trump has polarized the electorate around issues of immigration and race.

On key cultural issues, these well-educated non-evangelical whites lean almost as sharply toward the left as evangelicals do toward the right. In the religion institute survey, two-thirds of the college-educated whites who are not evangelicals rejected the idea that whites face as much discrimination as minorities; more than three-fourths disagreed that immigrants are "invading" America. Nearly three-fourths of them said it's not necessary to believe in God to be moral. A 55% majority of them said racists have taken over the Republican Party, while 59% rejected the idea that socialists now rule the Democratic Party.

On Trump, almost three-fourths of these non-evangelical college whites said he has damaged the dignity of the presidency. Two-thirds of them say they disapprove of his performance in office and more than three-fifths said they would support not only his impeachment but also his removal from office.

The working-class whites who are not evangelicals occupy a potentially pivotal space between these two opposing -- and roughly equal size -- groups of evangelicals and non-evangelical college-educated whites. The non-evangelical blue-collar whites display mixed instincts on racial and cultural issues. A slight majority of them agree that whites face as much discrimination as minorities, and an even narrower majority support building Trump's proposed border wall. But only a little more than two-fifths of them agree that immigrants are "invading" America, a perspective that draws vastly more agreement among non-college whites who are evangelicals.

Their views on Trump are similarly conflicted. More than half of the blue-collar non-evangelical whites say he has damaged the dignity of the presidency -- about twice the level of concern expressed by the non-college evangelicals. Support for impeaching and removing him from office reaches 43% among the men and 46% among the women. And they closely divide over his job performance: 55% of the men, but only 45% of the women, give him positive grades. On both of those measures, they are far more likely than the blue-collar white evangelicals to express negative views about Trump.

Two other new surveys offer further insights into what these patterns might mean for 2020. One is the new Nationscape project , a weekly survey of 6,000 Americans conducted by the Democracy Fund's Voter Study Group and two political scientists at the University of California at Los Angeles. At my request, the project combined results of its surveys from mid-July to late October to explore early preferences among these groups in a potential 2020 race between Trump and former Vice President Joe Biden.

That analysis showed Trump maintaining generally solid support among evangelical Christians. (He did, however, show some signs of potential slippage among evangelical women with college degrees compared with his showing among them in the exit polls for the 2016 election.) At the other end of the white education and religious spectrum, the Nationscape results showed Biden posting an advantage of more than 30 percentage points among college-educated white women who are not evangelicals and a nearly double-digit lead among the equivalent men. Each of those results was roughly the same as Hillary Clinton's performance in 2016, according to exit polls.

Compared with the 2016 exit polls, the Nationscape results showed Biden posting his biggest gains among the non-evangelical blue-collar men (trailing Trump among them by just 4 percentage points, compared with Clinton's much larger 23-point deficit in 2016) and the equivalent women: They preferred Biden by 10 percentage points in the Nationscape results, double Clinton's lead last time.

Warning signs in Wisconsin

Warning signs also emerged for Trump about his standing with non-evangelical whites without college degrees in recent polling in Wisconsin, the state that many believe could prove decisive in 2020. Those voters represent the state's largest single block: They make up just over 44% of Wisconsin's electorate, with the women slightly outnumbering the men, according to cumulative poll results from the Marquette University Law School poll provided by Charles Franklin, a pollster and professor of public policy there. (White evangelicals represent just under one-fifth of the state's voters and non-evangelical college-educated whites about one-fourth. Minorities compose the remaining roughly one-tenth of voters in Marquette's surveys.)

As in the national numbers, Trump retains very high approval ratings among white evangelicals in Wisconsin, though with some signs of erosion among those holding college degrees, according to cumulative results from the four most recent Marquette surveys that Franklin provided. In a hypothetical 2020 matchup against Biden, Trump still leads big with white evangelicals, especially the men without college degrees among them, according to combined results from surveys in August and October.

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The mirror image is that in Wisconsin, as nationally, Trump faces resounding disapproval among the college-educated whites who are not evangelicals, particularly the women: More than two-thirds of them give him negative marks. Those women now prefer Biden over Trump for 2020 by nearly 3 to 1; Biden posts a solid double-digit advantage among the men as well.

But the working-class whites who are not evangelicals are more conflicted: 53% of the men say they approve of Trump's performance, while 59% of the women say they don't. In an October survey, the Marquette poll found that while two-thirds of these men oppose Trump's impeachment and removal, the women split almost exactly in half on whether he should be ousted.

Matched against Biden, Trump leads among the non-evangelical blue-collar men by 10 percentage points, but trails by nearly 30 points among the women. (By contrast, Trump led in the survey by 40 points among the evangelical non-college white women.)

Most Democratic strategists agree that against Trump, the party has only limited opportunities for inroads among blue-collar white men, whether or not they are evangelical Christians. But they generally see a much greater opening among those white, non-college, non-evangelical women -- who some party strategists, slightly tongue in cheek, call WNCNEW

Even compared with the blue-collar non-evangelical men, those women generally express more concern about Trump's behavior and temperament and a greater sense of economic anxiety: In the Public Religion Research Institute survey nearly 3 in 5 of them said they would have trouble pulling together $400 to pay for an emergency, a higher share than any other group of whites. In the 2018 midterm elections, these women moved sharply toward Democratic candidates in House races, according to the exit poll results.

Finding a nominee who can consolidate those gains -- especially in Pennsylvania, Michigan and Wisconsin, the pivotal Rust Belt states that Trump captured in 2016 -- might be the shortest path back to the Oval Office for Democrats next year.