Successful Defections: Factionalism Under Mixed-Member Electoral Systems

• In Event: Electoral Systems and Voting Rules

Abstract

Do mixed-member electoral systems (MMS) promote party factionalism under presidential systems? Recent scholarship argues that factionalism under MMS stems from competition for the executive office. However, these arguments fail to explain outcomes under strong presidencies, where competition for the executive office is high and elites are vying for power within the party leadership. This paper argues that when popular support for the president is high and the governing party expects to receive large voter support in the legislative elections, MMS provides particularly high institutional incentives for members from losing factions (i.e. those outside the president’s faction) to defect and form a transitory electoral alliance. The formation of transitory alliances is less costly for losing factions under MMS because of the benefits conferred by running under a new alliance name: not only are alliance members better able to secure nomination in the single-member district (SMD) tier, but they are also able to increase the likelihood that alliance members will win votes in the proportional representation (PR) tier. To test this argument, I examine transitory electoral alliances that occurred in the 2008 South Korean Assembly elections, where governing party members who lost the nomination to members of the president’s faction decided to form an electoral alliance mobilized around Park Geun-hye, who was then a popular conservative party leader. Using geocoded polling station data, I exploit quasi-random variation in geography when estimating the effects in the South Korean Assembly elections. Focusing on polling stations in neighborhoods that were most adjacent to each other at the electoral district boundary, I compare PR vote shares between districts where a candidate from Park’s Alliance was nominated and districts where no candidate was nominated. This geographic variation allows us to minimize confounders which arise due to parties strategically placing a SMD candidate in districts where they expect to receive more votes. My findings show that members of the Park Alliance were able to significantly increase their representation in districts where they ran a candidate in the SMD tier, an effect which largely stems from a decrease in the PR vote share for the governing party. The findings of this paper contribute to existing theories of party nominations under strong presidencies.

Author

• Shinhye Choi, University of California, Berkeley