During the Depression, the Townsend movement enjoyed varied success in seeking pensions for the aged. Social-movement models predict that success depends on the mobilization of resources or on collective action. Other theories predict that economic or political conditions cause the emergence of movements and changes in public spending. The political mediation model used here holds that, to succeed, a movement must reinforce political action with strong organization of members under favorable political conditions. This article defines "success" and employs various analytical and empirical strategies, including qualitative comparative analysis on state-level data, to appraise the models. Although each perspective has some support, the political mediation model offers the best explanation of the patterns of successes. The state and the political party system determine whether mobilization and action benefit a constituency and win acceptance for a movement organization.