This chapter uses process tracing to argue that organizations that grant voice and veto power to activists in the decision-making process avoid oligarchization of the party. The FA presents an opportunity to analyze how party organization per se affects the performance of political parties. The FA is a successful case of party building and reproduction that sheds light on the role organizational structure plays in reproducing activists. The process tracing systematically describes and explains the formation and reproduction of the party. It shows how the party´s first steps as a political organization established a reproduction mechanism with a lock-in effect that explains the persistence of the party’s activism.

Uruguay’s Frente Amplio (Broad Front, FA) is a mass-organic institutionalized leftist party. It is a deviant case that helps explicate the reproduction of mass-organic party organization and activism. The peculiar internal structure of the FA and the rules that ensure a role for grassroots activists in the highest decision-making bodies of the party are a product of the extraordinary conditions that existed at the time of the party’s birth in 1971. The intense autonomous activism that occurred during this stage acts as a historical cause. The decision-making authority of the grassroots activists, granted incrementally since the FA’s foundational stage, enables activists to block changes that reduce their power, engendering a lock-in effect and positive feedback. These rules grant FA activists a significant voice, which imbues activists´ participation with a strong sense of efficacy. This perceived efficacy operates as a selective incentive for activists to engage with the party. The chapter develops this theoretical argument and justifies the selection of the FA as a deviant case of party reproduction.