Party-switching convergence theorem

Abstract This paper develops a game-theoretic and dynamic framework to analyse how judicial manipulation by governing parties alters political incentives in multi-party systems. The model shows that biased legal enforcement can prompt politicians - even if innocent - to switch allegiance to the ruling party to avoid penalties, with decisions shaped by reputational, voter and institutional frictions. Strong frictions can sustain pluralistic equilibria despite judicial asymmetry, while weaker frictions or stronger incentives lead to a single-party convergence. Moreover, not only formal institutions limit the judicial weaponization but also by voters’ responsiveness to imbalances in enforcement. The model therefore highlights how even modest judicial biases can erode political pluralism over time, while also identifying the political and electoral conditions under which such dynamics can be contained.