One of the most important developments in American politics over the last 40 years has been the rise of negative partisanship—the phenomenon whereby Americans largely align against one party instead of affiliating with the other. Though it has the power to reshape patterns of political behavior, little is known about the microfoundations driving negative partisanship. In this article, we show how the growing racial divide between the two major parties, as well as the presence of partisan‐friendly media outlets, have led to the rise of negative partisanship. We also utilize the growing literature on personality and politics to show how the Big Five personality traits are predictive of negative partisanship. The results suggest that the psychological roots of negative partisanship are both widespread and, absent drastic individual and structural‐level changes, likely to persist.