The average cost of a wedding in 2016 was $35,329, a $2,688 increase from the year before, according to a survey of 13,000 brides and grooms conducted by wedding website The Knot. That might come as a shock considering that it’s only $6,000 less than the median annual income for full-time workers in the U.S. That is, the average American would have to spend nearly an entire year’s worth of earnings to pay for the typical American wedding.

The data reflects a troubling demographic shift in American culture: While marriage rates are down across the board, the marriage rate for relatively poor, non-college-educated Americans has fallen more precipitously, meaning marriage is increasingly the province of the middle and upper classes.

The trend seems counterintuitive given the tax and financial benefits to marriage. If anything, marriage would seem more appealing to economically distressed populations. But the labor crisis that’s plaguing blue-collar men has resulted in a severe drop in the marriage rate among lower-class Americans, and a lot of pissed off poor men and women.

To better understand the causes and ramifications of this drastic change, MEL speaks with University of Minnesota law professor June Carbone, co-author of Red Families v. Blue Families. Carbone explains how the marriage class divide is rooted in access to education, birth control and the state of blue collar labor—and how that’s reflected in the Trump presidency.

Answers have been edited and condensed for clarity.

When did this shift start?

We date it back to 1990. If you go back to the divorce revolution in the 1970s, there was an explosion in divorce. But divorce rates for college graduates decline substantially after that. By the time you get to 2004, divorce rates for college-educated couples are down to what the divorce rate was in 1965.

When you look at non-college-educated couples, however, there’s a small drop in the divorce rate after 1970. But in 1990, their divorce rate starts increasing again, at the same time it’s dropping for college graduates.

What does that indicate?

That lower-class relationships were becoming less stable.

There are two kinds of relationships that produce stable marriages:

Patriarchal: The husband earns more, and he trades his income for custody rights to the children. He’s the head of the family; she takes care of the household. If they divorce, she gets a share of his savings, while he gets custody. They both see it as a good deal. Egalitarian: The second model is both spouses are in the workforce and both have a good income. And both help out with the kids, taking them to doctor’s appointments and dropping them off at soccer practice.

The second model is how we think of the modern marriage. But it requires a high degree of stability and trust, and that trust isn’t there among lower-class couples. Lower-class men are having a harder time staying employed, and it’s hard to trust someone with uncertain financial prospects.

What other factors play into this class divide with respect to marriage?

For one, fewer college-educated women get pregnant when they’re young.

If you look at marriages before the 1970s, many of them were triggered by unplanned pregnancies. By the late ‘70s, birth control is more accessible, and you see a corresponding jump in the average age for a first marriage. By the time Americans settle down, get married and have kids, they’ve already invested in their careers and figured out who they are as people. Instead of marrying your college sweetheart who accidentally got you pregnant, you marry someone when you’re 30 years old and a fully realized person. There’s more trust in that scenario.

But for women who didn’t go to college, the average age of pregnancy doesn’t change very much. And while they’re still getting pregnant at a young age, they’re not getting married as often. In the 1980s, this population would have gotten pregnant, married the father, then divorced him. Starting in the ‘90s, they got pregnant but didn’t marry the guy.

But why didn’t they marry the guy? You’d think that poor women would want to get married more because of the financial benefits.

There wasn’t a financial incentive to get married, though, because of the decline in blue-collar jobs starting in the ‘90s. The high-paying blue-collar jobs disappeared.

It’s not just that blue-collar men are more likely to be unemployed (they are). It’s not just that their incomes declined (they did). It’s that their employability became much more unpredictable, and that’s not grounds for a stable relationship. When there aren’t many men worth committing to, women commit to themselves.

So blue-collar men have lost their value in the marriage market?

I’m saying something else. I’m saying there’s a behavioral effect on blue-collar women, as well. There’s an unhappiness that sets in.

Now, blue-collar American women have to work. They didn’t have to in the 1950s. They don’t have the option of not supporting themselves. And it creates this unhappiness in blue-collar women that started in the ‘90s and accelerated afterward.

The man is earning less, but he still expects the woman to do the housework. But he’s not contributing as much money as the woman thinks is appropriate, so she’s really unhappy. And unemployed men actually tend to do less housework than ones who have jobs, because they just end up moping around. So she really resents him, and they don’t get married as often.

Why the hell don’t unemployed men do more housework?

The farther down the economic ladder, the more traditional the marriage arrangement. Both lower-class men and women think if they get married, she’s going to do the bulk of the housework. But if they’re single and just roommates, the responsibility doesn’t fall to her.

It’s counterintuitive, because you’d think wealthy, financially independent people would be more willing to forsake marriage.

That’s what everyone predicted, including Nobel Prize winner Gary Becker, but they were wrong.

So why do rich people still want to get married?

Marriage is kind of a status symbol for the rich now. There’s this cultural shift among upper class, where high-status men want to marry high-status women. Their ideal partner is a professional woman who’s close to your equal (but who won’t show you up). Mark Zuckerberg marries a doctor, for instance. In fact, the only group in American society for whom marriage rates have gone up are the top 10 percent of women in terms of income, mainly because ultra-rich men find them so desirable.

That defies the archetype of the rich, successful career bachelor.

Better-off men are still wary of marriage, but so are poor women. For instance, when you look at college-educated 20-something couples living together, two-thirds of the women say they plan to marry, but only one-third of men do. But if the group that doesn’t have any college education, the numbers are reversed: two-thirds of the women say they don’t plan to marry the current partner, but only one-third of the men say they don’t.

What does this mean for the public health of lower class communities?

It’s bad. Parents are less invested in their children, and the instability is bad for the kids.

How does the class divide over marriage speak to our current political moment, where there’s so much animosity between the so-called “elites” and “real Americans”?

Blue-collar men see themselves as on the losing end of this marriage trend. You have a lot of low-class men who got booted out of their homes by women, and they’re angry. And when you look at Trump’s base, it’s a lot of angry white men.