Past work on the political impact of racial diversity has focused on direct effects, demonstrating that diverse environments are associated with more negative - or in some circumstances, more positive - racial attitudes and race-targeted policy preferences. We show that diversity functions in a second way, as a variable that magnifies the political impact of individual differences in the psychological disposition of authoritarianism. Using a national sample, we find that in white areas with minimal diversity, authoritarianism had no impact on racial prejudice, political intolerance, and attitudes toward immigration. As diversity rises, however, authoritarianism plays an increasingly dominant role in political judgment. In diverse environments, authoritarians become more racially, ethnically, and politically intolerant and nonauthoritarians less so. We conceptually replicate these findings in a dorm setting with plausibly exogenous levels of local diversity and discuss the implications of our findings in terms of the various ways in which ethno-racial diversity structures political attitudes.