Who Mobilizes When Others Protest? The Seesaw Effect of Tactic Efficacy Beliefs in Social Movement Diffusion

When does protest in one domain catalyze activism in another—and when does it divert potential activists from their own causes? Prior research on the diffusion of protest has overlooked how the collective beliefs of dormant populations—those not yet engaged in activism—may influence their participation. We argue that exposure to protest sends a dual signal—about both issues and tactics—and that its effects depend on tactic efficacy beliefs: shared beliefs about whether protest tactics can achieve social or political change. We theorize that exposure to protest produces a "seesaw effect": it redirects mobilization away from the focal cause in high-belief communities while activating protest participation in low-belief, previously dormant ones. We employ a shift-share instrument (SSIV) to estimate the causal impact of social movement mobilization exposure on real-world labor movement mobilization activity based on 2.6 million news stories across 14 social movements, and measure tactic efficacy beliefs using 1.6 million online posts from 29,000 rideshare drivers. Our conceptualization of tactic efficacy beliefs contributes by developing a novel explanation for the conditions under which protest spreads—or stalls—across issue domains.