Surprising: Reelection Incentives Strengthened Party Unity in Mexico

Why This Question Matters

Scholars often argue that incentives to cultivate a personal vote weaken party unity, because legislators respond to local electoral pressures rather than party leadership. Lucia Motolinia Carballo tests a countervailing idea: when parties control ballot access and the resources candidates need to build personal votes, they can use those levers to reward loyalty—so giving legislators the chance to be reelected may actually increase party discipline.

What Lucia Motolinia Carballo Did

The paper exploits the staggered rollout of Mexico’s 2014 Electoral Reform, which for the first time allowed consecutive reelection for state legislators. Using a difference-in-differences design, the study compares legislative behavior before and after the reform across states where the changes took effect at different times, covering the period 2012–2018.

How Legislative Unity Was Measured

• Position-taking: correspondence analysis applied to a newly assembled corpus of over 500,000 legislative speeches from twenty Mexican states.
• Roll-call behavior: analysis of more than 14,500 roll-call votes across fourteen states during the same period.

Key Findings

• Contrary to the expectation that reelection fuels personalization and fragmentation, the reform’s reelection incentives increased intra-party unity on both speech content and roll-call voting.
• These patterns are consistent with the theory that parties, by controlling ballot access and campaign resources, can condition future access on legislators’ loyalty and thus bind legislators to party agendas.

Implications for Electoral Reformers

The results suggest that institutional efforts to personalize politics—by enabling reelection—do not automatically erode party cohesion. Where parties retain control over candidate resources and ballot access, extending reelection can strengthen party discipline. This finding has direct relevance for countries considering reforms that change legislators’ electoral incentives while leaving party gatekeeping power intact.