On July 19, 2023, the federal antitrust agencies—the US Department of Justice (DOJ) and the Federal Trade Commission (FTC)—released draft Merger Guidelines (dMGs) for public comment.1 Once these guidelines are finalized, they will be the official statement of US antitrust enforcement policy toward corporate mergers. This policy brief addresses how government policy delineates the relevant market in which the likely effects of proposed mergers are evaluated. It argues that the dMGs abandon critical principles, which signals a return to the gerrymandering that characterized merger cases in the 1960s.