Donald turner, America’s top trustbuster in the mid-1960s, saw antitrust law as benefiting from an “inhospitable” tradition: on many matters its default response was to say no. Government lawyers routinely blocked mergers merely on the grounds that the resulting company would be too big. The companies’ counterargument that being bigger would make them better was rarely entertained by the courts.

In the 1970s the “Chicago school” of antitrust law successfully harnessed economics to argue for a much more hospitable approach. Over the following decades America’s regulators became so welcoming that critics painted them as doormats. In many industries the largest firms have consistently gained market share without any official concern; the most successful technology companies have grown into veritable titans. Many economists studying the subject now worry that a lack of competition is an economic drag, especially online. Some scholars go further, arguing that the Chicago school’s sense of what is good for consumers is not serving their broader interests.

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There are, broadly speaking, two sets of ideas for reforming competition economics and antitrust enforcement in response to these worries. Adherents of the more radical call themselves “neo-Brandeisians” after Louis Brandeis, an early-20th-century American Supreme Court justice who thought the overarching purpose of government antitrust action should be to prevent any one firm from exerting too much power over the economy. Neo-Brandeisians such as Lina Khan of Columbia Law School and Matt Stoller of the American Economic Liberties Project, a think-tank, want to broaden the purpose of antitrust investigations beyond promoting consumer welfare. Governments, they argue, should not fear breaking up the tech giants; they should fear leaving them be. In this view the companies’ size and power are a threat not just to consumers and workers but to democracy itself.