Abstract

We study how party discipline varies with electoral mandates and career concerns. In our model, partisan benefits induce discipline insofar as leaders rally enough support among their legislators to make their promises credible. Absent reelection, constituency concerns offset the leader’s promises, leaving district legislators less disciplined than their list copartisans. Reelection makes these benefits electorally valuable, directly improving district legislators’ local valence and list legislators’ renomination prospects, and indirectly strengthening the leader’s credibility in both tracks. We test the empirical implications of the model in Mexico’s mixed-member Congress around the reform introducing consecutive reelection. We measure disagreement with party leaders in votes and speech across seven Congresses (2006-2024): disagreement falls in both tracks after the reform, most among district incumbents. Leaders, in turn, redirect partisan benefits toward district incumbents ex ante and reward the disciplined while punishing dissenters ex post. Accountability reforms that leave ballot access, list placement, and campaign finance in party hands can strengthen the organization they were meant to check.


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