Abstract Populist leaders and movements are incredibly diverse, but one factor that most share is the tendency to pick fights. Populists often stir up conflict and use aggressive rhetoric that would destroy the reputation of mainstream politicos. Furthermore, many of these fights have little material benefit for base-level supporters, and often actively harm them. Yet populist militants generally reward combative behavior. Why is populism so conflict prone? And why do populists so often escape negative consequences for provoking damaging dustups? I argue that these sorts of conflict are driven by an emotional impulse that lies at the heart of populism: punitive aggression. Populists view political problems as the result of malign actions by hostile outgroups, and they perceive the state as either negligently allowing or actively abetting these actions. The failure of the state to punish the guilty breeds an intense and deep-seated desire to harm those seen as violating norms and values, regardless of the cost. Observational and experimental data are consistent with the hypothesis that, while the never-ending conflict typical of populism may harm its adherents’ interests, it continues because it satisfies much more basic emotional and psychological needs. This paper suggests that confronting and challenging populists may be difficult because forceful responses will reinforce the bond between the leader and his or her followers.