America is no longer a majority Protestant nation. In fact, one-fifth of the country now identifies as either "nothing in particular," agnostic or atheist. That's the conclusion of a new Pew Forum on Religion and Public Life survey released this week.

The general decline of Protestants is an old story, though dropping below the majority threshold will surely set off much discussion about the changing character of the nation. For many decades now, Mainline Protestants—Methodists, Presbyterians, Episcopalians, Lutherans, and others—have been in steep decline. They have been replaced in part by Evangelical and independent churches that do not have the same kind of centralized institutional structures, but apparently the megachurches are not filling fast enough to maintain a Protestant majority.

One is tempted to attribute the growth in the unaffiliated to the influence of secular elites replacing any residual traces of the old mainline WASPs, but a look at the typical proxies for social status—education and income—suggests that unaffiliated people are relatively evenly distributed along class lines. Whether you've been to college or are financially comfortable, there's about the same chance you go to church as someone who is poorer or less educated.

The unaffiliated aren't what we typically think of as secular, either:

Just 5% say they attend worship services on a weekly basis. But one-third of the unaffiliated say religion is at least somewhat important in their lives. Two-thirds believe in God (though less than half say they are absolutely certain of God’s existence). And although a substantial minority of the unaffiliated consider themselves neither religious nor spiritual (42%), the majority describe themselves either as a religious person (18%) or as spiritual but not religious (37%).

Though a fall in church attendance doesn't seem to suck all the spirituality out of the air, the decay of America's strong church institutions might still be a cause for concern. The famous nineteenth-century observer of American social conditions, Alexis de Tocqueville, saw the strength of mediating institutions—churches and other civic organizations—as the glue that held society together without the need for an oppressively large state. These organizations also served as the first rung of the social safety net. Even those not fond of going to church seem to agree with Tocqueville, with three-quarters "of unaffiliated saying religious organizations bring people together and help strengthen community bonds (78%) and a similar number saying religious organizations play an important role in helping the poor and needy (77%)."

To the secular-minded observer, strong religious affiliation may look like an undesirable tribalism that Americans would do well to move beyond. But if Tocqueville was right, the crumbling of the Protestant denominations may leave a void that is difficult to fill—except perhaps with a large and expensive state.