Marriage today is fracturing along class lines. Americans with four-year college degrees continue to wed in large numbers and enjoy stable marriages. But only about a third of American adults hold four-year degrees. For the larger number of Americans without a college degree, marriage is disappearing with alarming speed.

For example, only about 6% of American women with four-year college degrees today are having children outside of marriage. But for those with high school degree only, the number is 44%. For high-school dropouts, it’s 54%.

Since the 1970s, there’s been virtually no change in the likelihood that a teenage girl born to well-educated parents will grow up in an intact family. But for girls born to moderately-educated (high school, but no four-year college degree) parents, the chance of living in an intact home has dropped 16%.

Many other numbers bear out this large and growing class-based marriage divide — a divide that cuts across all racial boundaries.

This problem ought to be a core liberal issue, right up there with income stagnation and inequality. Why? One simple reason: To a considerable extent, income stagnation and inequality are the marriage problem.