When Reelection Increases Party Unity: Evidence from Parties in Mexico

It is often argued that when legislators have personal vote-seeking incentives, parties are less unified because legislators need to build bonds of accountability with their voters. I argue that these effects depend on a legislator’s ability to cultivate a personal vote. When parties control access to the ballot and the resources candidates need to cultivate personal votes, they can condition a legislator’s access to these resources on loyalty to the party’s agenda. I test this theory by conducting a difference-in-differences analysis that leverages the staggered implementation of the 2014 Mexican Electoral Reform. This reform introduced the possibility of consecutive reelection for state legislators, increasing their incentives to cultivate personal votes. I study unity in position-taking and voting behaviour of Mexican state legislators from 2012 to 2018. To analyze position-taking, I apply correspondence analysis to a new dataset of over half a million legislative speeches in twenty states. To study voting, I analyze over 14,500 roll-call votes in fourteen states during the same period. Results show that reelection incentives increased intra-party unity, which has broad implications for countries introducing electoral reforms aiming to personalize politics.