Today, much of that Tocquevillian ecology—which lasted well into the mid-20th century—has withered away. What remains, as sociologist Robert Sampson shows in his research on “neighborhood effects,” underscores the concentration of wealth and social capital that caused the withering.

Consider how much PTAs do for affluent public schools in your town and how little they do for impoverished ones. Consider how few low-wage workers become officeholders or organizational leaders. There are fewer places in America now to assert a claim of civic dignity that can counter the experience of economic indignity.

Trump and Sanders have successfully exploited the resulting resentment. But neither of them—indeed, no candidate in either party—has tailored a sophisticated agenda in response to it. Fortunately, we have a useful precedent. A century ago, at the dawn of another Gilded Age of pernicious bigness, Louis Brandeis laid out a solution to self-perpetuating concentrations of power: a politics against monopoly.

Brandeis, a pioneering legal activist who served on the Supreme Court from1916 to 1939, recognized that while many capitalists praise competition, what they want really is monopoly—and that true competition, in which more people get more of a chance to challenge entrenched winners, should be the object of public policy.

True competition—now, as then—requires recognition that economies and communities are not static mechanisms. They are complex adaptive systems, in which both advantage and disadvantage compound. It’s not just that the rich get richer and the poor poorer; it’s that the rich get louder and poor quieter.

This amalgamation of market power, political voice, and social mobility is the natural outcome of a system left to itself—of laissez-faire ideology. True competition demands an economic and civic program of actively busting “opportunity monopolies” and recycling the unearned privilege that comes with them.

Brandeis articulated such a program and put elements of it into place both as a “people’s lawyer” and as a jurist. What would a 21st-century agenda look like? It would focus on anticompetitive acts not only in the economy but also in the polity.

There are elements that much of today’s left would like: A much more robust inheritance tax. A progressive funding source for public schools delinked from property values. Higher wages for the working poor, and easier ways for workers to organize and bargain. Democracy vouchers, like the public campaign-finance system just enacted in Seattle to give everyday voters more power to be donors. Capital requirements for banks and a “size tax” for financial institutions. Antitrust enforcement that promotes competition and not just efficiency.

There are also elements many on the right would favor: Unwinding corporate subsidies and cronyism on Wall Street and in government contracting. A radical simplification of the tax code so that tax breaks no longer flow overwhelmingly to affluent families. Changes to union contracts that make it easier to replace poor performers. Limits on the scale of government agencies so that they don’t become “too big to serve.”