Threat theory argues that states toughen criminal laws to repress the competitive power of large minority groups. Yet, research on threat suffers from a poor understanding of why minority group size contributes to social control and a lack of evidence on whether criminal law is uniquely responsive to the political interests of majority racial groups at all. By compiling a unique state-level dataset on 230 sentencing policy changes during mass incarceration and using data from 257,362 responses to 79 national surveys to construct new state-level measures of racial differences in punitive policy support, I evaluate whether criminal sentencing law is uniquely responsive to white public policy interests. Pooled event history models and mediation analyses support three primary conclusions: (1) states adopted new sentencing policies as a nonlinear response to minority group size, (2) sentencing policies were adopted in response to white public, but not black public, support for punitive crime policy, and (3) minority group size and race-specific homicide victimization both indirectly affect sentencing policy by increasing white public punitive policy support. These findings support key theoretical propositions for the threat explanation of legal change and identify white public policy opinion as a mechanism linking minority group size to variation in criminal law.