Don't write the obituary yet. A groundbreaking new study by Brookings Institution scholar Julia Isaacs brings us good news: Two-thirds of us who were children in the late-1960s have grown up to earn more (adjusted for inflation) than our own parents did at the same age. By 2006 the median family income of the adults in this study was $71,900, up 29 percent compared to the median income of their parents in 1968.

But the income gains are not equally shared. Between 1974 and 2004, the racial gap in median family income actually widened, with black family income dropping from 63 percent to 58 percent of the median white family income.

Why?

First consider personal earnings. Between 1974 and 2004, the incomes of white men dipped slightly from $41,885 to $40,081. Black men's personal earnings dropped more dramatically from $29,085 to $25,600. Meanwhile, white women's income quintupled from $4,021 to $22,030, while black women's personal earnings only doubled, from $12,065 to $21,000.

White men would be downwardly mobile, except that they support fewer kids than their fathers' did, and their wives earn far more. The number of angry white blue-collar males would be far higher, in other words, if they weren't married to pink-collar earning wives.

It's not hard to see storm clouds brewing in these stats. How long before stagnating white male wages create some kind of visible political backlash? After all, blue-collar guys don't have any more wives to send out into the workforce, and how many fewer kids can women have? Economic populism may not be dead, just sleeping.

But black women were already in the work force in large numbers by 1968, so the feminist revolution had less dramatic returns for black families. And for blacks, declining male wages interacted with the sexual revolution to create an intergenerational disaster for African-American children.

How big a disaster? Take as a proxy for the middle-class: American parents who earned in the middle quintile (or 20 percent) of Americans in 1968. More than two-thirds of white children in this income group grew up to earn more than their parents did at the same age. By contrast almost three-fifths of black children in the middle income group earned less than their parents did.

The American Dream plays a lot better in white than black.

The "marriage gap" between white and black plays a big part in this story. African-Americans are much less likely than their parents were (or than white adults are now) to be married. They are also more likely to have children outside of marriage than their parents were, or than white adults are today.

When 25 percent of children in a community are born outside of marriage (as among whites today) that's a serious problem. When almost 70 percent of children in a given community are born outside of marriage (as among African-Americans today) that's a tsunami blocking the intergenerational accumulation of human and social capital.

So far, the silence about the issue among our leaders is deafening. Hillary, Barack, Fred, Mitt, Rudy: Who will take up the challenge of reducing the marriage gap written so starkly in black and white? Who wants to rebuild the American Dream for all our children?