Political collective action requires assembling and motivating supporters. Many theories view emotions as functional tools for managing relationships, including within groups. We study what leads citizens to use the emotions anger and gratitude as social pressure. Specifically, we test what determines the use of these emotions to prevent potential exiters from leaving a political group and to encourage potential recruits to join. Because parties are enduring social affiliations (compared to transient or issue-focused groups), we predicted that partisans would express stronger emotions. We tested this proposition in two separate studies—one an observational study featuring a representative sample of US adults and one an experimental study conducted in Denmark. As predicted, people with a partisan mindset, whether naturally occurring or experimentally manipulated, felt more anger and gratitude at potential exiters and recruits. Citizens strive to fortify and expand their ingroups and sometimes use emotions as social pressure to do so.