How do firms' strategic decisions affect the emergence and evolution of activism? We examine this question through a study of protests against nuclear power plants in the United States. We find that the decision to cancel construction of a nuclear unit—a substantial victory for activists—is associated with an upsurge in antinuclear protest activity, as emboldened activists stay mobilized even once the level of threat abates. We also find that when a firm decides to complete a nuclear power plant, thereby marking a defeat for activists, antinuclear protests wind down and we witness an increase in mobilization towards other causes. We discuss the implications of our findings for the study of the interaction between social movements and firms.