Why do some religious parties survive after adopting a moderate ideological outlook while others do not? The rise and fall of religious parties since the onset of democratic transition in Indonesia has set off an intriguing debate over the role and future of political Islam in electoral politics. This article seeks to explain the diverging – and unexpected – trajectories of the two most prominent religious parties, the National Awakening Party (PKB) and Justice Prosperous Party (PKS) through a close examination of the case of PKB. It emphasizes organizational qualities to advance two claims. First, the decline of the moderate PKB is the result of the permeation of personality-based clientelistic and ascriptive relations as well as lack of party institutionalization. Political survival of the puritanical Islamist PKS, on the other hand, is explained by organizational cohesion achieved through party institutionalization. Second, a disciplined party structure has allowed PKS elites to achieve controversial ideological adjustments. In short, a moderate centralist religious ideology or outlook alone is not sufficient to achieve political survival in the competitive environment of electoral and religious politics.