Scholarship on regulatory capture—when businesses lobby regulators to act contrary to the public interest—has thrived since the 1970s. Yet it ignores an important dimension of influence, what we call ideological capture. This occurs when experts design regulatory frameworks that marginalize important public values and produce favorable outcomes for special interests even in the absence of lobbying. We present a theoretical and empirical framework for understanding ideological capture, rooted in expert–public cleavages, and measure its presence in an important policy domain (antitrust review of business mergers) with an original survey of the public and of antitrust lawyers. Our results suggest that the main framework for evaluating anticompetitive conduct, the consumer welfare standard, marginalizes important public concerns but is deeply popular among antitrust lawyers. With prior work showing the standard arose not from conventional processes but from judicial and bureaucratic activism, we conclude that antitrust policy evidences ideological capture.