Antitrust populists increasingly call on the government to “break up big tech.” But antitrust enforcers would face heavy evidentiary burdens if they sought to break a company up on the premise that a long-consummated merger was unlawful from the outset and should have been blocked years ago....

We clarify and defend the Chicago School of antitrust against incorrect and uninformed claims that it represents a narrow set of inefficiency impossibility theorems based on free market ideology. The Chicago School arose decades ago as a reaction to the then current antitrust policies. Chicago...