(CNN) With his sharp words in recent days defending men accused of sexual harassment and spousal abuse, President Donald Trump launched another firebomb into the cultural chasm running through his presidency.

This new debate could expose Republicans in 2018 to a more widespread backlash among women -- and a more pointed gender gap -- than the party has confronted in almost any recent election.

Trump's praise of former White House aide Rob Porter, who was accused by both of his ex-wives of abusing them, and his tweet this weekend arguing that the backlash against men accused of sexual harassment has gone too far, reinforced his central cultural message as president.

With both comments, Trump was sending the same signal that he has with his push for new restrictions on not only undocumented but also legal immigration; his criticism of NFL players who don't stand for the national anthem; and his rescinding of the protections for transgender military members that former President Barack Obama had established.

On all of these fronts, Trump is addressing the substantial portion of his " coalition of restoration " that fears American society is changing too fast -- economically, demographically and culturally. In the process, he's infuriating the elements of the Democratic " coalition of transformation " that most welcome all of those changes -- particularly minorities, single and college-educated white women, and Millennials.

The key political question is whether his more open questioning of the #metoo movement to confront sexual harassment and violence will also strain his already fraying hold on the women voters in his coalition, particularly those without a college degree.

Those women tend to hold views about changing gender roles that are more conservative than those of college-educated and Democratic-leaning women, but more liberal than those of non-college and Republican-leaning men.

Working-class white women drawn to Trump "are facing a cross pressure where they are with him on the hardline immigration stands, but are not sure about his views on women," said Daniel Cox, research director for the non-partisan Public Religion Research Institute, which extensively studies Americans' attitudes on social questions. "It's hard to know what issue will take priority."

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Evidence that under Trump, gender divisions over politics are widening

Since the 1980s, political analysts have focused enormous attention on the gender gap -- the tendency of women to vote more Democratic than men (or conversely, men to vote more Republican than women). But over that period, the differences among women have often been greater than the differences between women and men.

In the presidential races from 2004 through 2012, for instance, the Democratic nominees ran at least seven points better each time among white women with a college degree than those without one; in each instance, that was as least as large as the gender gap between white women and white men. Across those three elections, the difference between the Democratic candidate's showing among married and single white women was larger each time than the voting gap between white women and white men.

In 2016, the overall gender gap widened to its highest level since at least 1980: Hillary Clinton ran 13 percentage points better with women than men. But the gap was so large not because she ran particularly well among women: in fact, she drew a smaller share of the white female vote than the Democratic nominees did from 1996 through 2008.

Mostly the gender gap was so pronounced because Clinton posted historically low numbers with white men, especially those without college degrees. Although Clinton ran well among African-American women and college-educated white women, Trump beat her badly among married white women, narrowed the usual Democratic advantage among single white women, and posted the best showing for a Republican among non-college white women since Ronald Reagan in 1984, according to exit polls.

Trump's success at carrying most white women against the first major-party female nominee showed the mistake of considering them a monolith through the all-encompassing prism of the gender gap. His inroads demonstrated that many blue-collar, evangelical, older and non-urban women responded to his nationalist, culturally conservative and anti-elitist messages -- just as the equivalent men did.

An array of polls shows that women in Trump's coalition take more conservative positions than Democratic-leaning and college-educated women not only on racially-tinged cultural issues such as immigration and civil rights, but also on gender-related questions about the proper roles of men and women.

In a 2016 PRRI/Atlantic survey, 40% of Republican-leaning women compared to just 28% of Democratic-leaning women, agreed that society is "better off when men and women stick to the jobs and tasks for which they are naturally suited."

In its American Trends Panel on-line survey , the Pew Research Center has likewise found big gaps between Republican- and Democratic-women over gender roles, relationships and parenting, according to previously unpublished findings provided to CNN.

In that survey, Pew asked about the impact of social changes that have seen "more women now work outside the home and more men ... involved with household chores." Democratic-leaning women were about twice as likely to say those changes had made it easier, rather than harder, to raise children; a plurality of Republican-leaning women said the changes had made raising children harder. Likewise, Democratic-leaning women by more than two-to-one said those changes had made it easier for a marriage to succeed; Republican-leaning women divided equally on whether the changes made it easier or harder. Far more Democratic- than Republican-leaning women in the survey said it was appropriate to encourage young boys to undertake activities usually associated with young girls.

On sexual harassment itself, a gap persists between Democratic- and Republican-leaning women. In a January ABC/Washington Post poll , Democratic women were much more likely than Republican women to describe sexual harassment as a "serious" problem for society (86% vs 61%.) Among Democratic women nearly twice many said the problem has not received enough, rather than too much, attention. By contrast, Republican women were three times as likely to say harassment has received too much, rather than too little, attention.

In the Pew survey, Republican women were far more likely than Republican men to say boys should be exposed to activities usually associated with girls, and modestly but measurably more likely to say changing gender roles made it easier to raise children and enjoy successful marriages.

As Trump solidifies his identification with the backlash against the sexual harassment movement, that space between Republican-leaning women and men could provide an opening for Democrats to widen the overall gender gap.

An erosion of support among women

When Quinnipiac University last November asked whether Trump respects women as much as men, Republican women (at 28% ) were essentially no more likely than Republican men (26% ) to say he did not.

But looking more broadly at white women without a college degree -- a critical swing constituency for Republicans --- 52% of them said Trump did not respect women as much as men, according to unpublished figures provided by Quinnipiac. That wasn't nearly as many as the 66% of college-educated white women who expressed that view about him, but it was considerably more than the 39% of blue-collar white men who agreed.

Compared to his vote in 2016, Trump's approval rating among those blue-collar white women has conspicuously declined. Trump won 61% of white women without a college degree in 2016, according to exit polls; but his approval rating among them tumbled to 48% in the full year 2017 average of Gallup polling . Among college-educated white women, he experienced a comparable fall from a much lower starting point: from 44% of the vote in 2016 to an ominous 32% average approval rating last year. With African-American women, Gallup put his 2017 approval rating at a microscopic 6%, virtually unchanged from his miniscule 4% vote with them in 2016. With Latino women, Gallup put Trump's 2017 approval at just 15%, down from his 25% showing in 2016.

Most analysts believe the biggest reason for this consistent pattern of significant decline among women across the board is that Trump's drive to repeal the Affordable Care Act and to pass a tax bill they saw as tilted toward the top has dented their confidence he will provide them more economic security. But polls also leave no doubt that many of these women have watched his volatile behavior as president with alarm.

The large block of white women uneasy about the changing gender roles identified with modern feminism presents a formidable barrier to Democrats hoping for big gains among blue-collar and older, much less evangelical or rural, white women in 2018 and 2020. But even relatively modest advances among those groups -- particularly blue-collar and older women across the Rustbelt -- could make a big difference in both elections. And by aligning so unreservedly with the men accused of sexual misconduct, rather than the women they have been alleged to victimize, Trump is raising the risks of such shifts.