Can political rallies affect the behavior of law enforcement officers towards racial minorities? Using data from 35 million traffic stops, we show that the probability that a stopped driver is Black increases by 5.74% after a Trump rally during his 2015–2016 campaign. The effect is immediate, specific to Black drivers, lasts for up to 60 days after the rally, and is not justified by changes in driver behavior. The effects are significantly larger among law enforcement officers whose estimated racial bias is higher at baseline, in areas that score higher on present-day measures of racial resentment, those that experienced more racial violence during the Jim Crow era, and in former slave-holding counties. Mentions of racial issues in Trump speeches, whether explicit or implicit, exacerbate the effect of a Trump rally among officers with higher estimated racial bias.