It’s not only that richer kids have become more active. Poorer kids have become more pessimistic and detached. Social trust has fallen among all income groups, but, between 1975 and 1995, it plummeted among the poorest third of young Americans and has remained low ever since. As Putnam writes in notes prepared for the Aspen Ideas Festival: “It’s perfectly understandable that kids from working-class backgrounds have become cynical and even paranoid, for virtually all our major social institutions have failed them — family, friends, church, school and community.” As a result, poorer kids are less likely to participate in voluntary service work that might give them a sense of purpose and responsibility. Their test scores are lagging. Their opportunities are more limited.

A long series of cultural, economic and social trends have merged to create this sad state of affairs. Traditional social norms were abandoned, meaning more children are born out of wedlock. Their single parents simply have less time and resources to prepare them for a more competitive world. Working-class jobs were decimated, meaning that many parents are too stressed to have the energy, time or money to devote to their children.

Affluent, intelligent people are now more likely to marry other energetic, intelligent people. They raise energetic, intelligent kids in self-segregated, cultural ghettoes where they know little about and have less influence upon people who do not share their blessings.

The political system directs more money to health care for the elderly while spending on child welfare slides.

Equal opportunity, once core to the nation’s identity, is now a tertiary concern. If America really wants to change that, if the country wants to take advantage of all its human capital rather than just the most privileged two-thirds of it, then people are going to have to make some pretty uncomfortable decisions.

Liberals are going to have to be willing to champion norms that say marriage should come before childrearing and be morally tough about it. Conservatives are going to have to be willing to accept tax increases or benefit cuts so that more can be spent on the earned-income tax credit and other programs that benefit the working class.

Political candidates will have to spend less time trying to exploit class divisions and more time trying to remedy them — less time calling their opponents out of touch elitists, and more time coming up with agendas that comprehensively address the problem. It’s politically tough to do that, but the alternative is national suicide.