Antitrust enforcement in the United States has declined since the 1960s. We investigate the political causes of this decline by looking at who made the crucial decisions and the strength of their popular mandate. Using a novel framework to understand the determinants of regulatory capture and several new datasets, we find that there was no public support for the weakening of antitrust enforcement. The decline in antitrust enforcement was the result of a collection of technocratic decisions made in politically unaccountable ways, mostly by regulators and judges. Behind the scenes, big business played a major role in influencing these agents; but other factors (like the increase in private sector pay relative to government pay) and intellectual currents mattered as well.The conventional wisdom is that an intellectual movement in economics that began at the University of Chicago, and spread to other universities like Harvard, revolutionized antitrust law by injecting a high degree of skepticism into antitrust analysis.