Party Dominance and the Logic of Electoral Design in Mexico’s Transition to Democracy

This paper discusses the role of electoral institutional design in Mexico’s transition to democracy. Our argument is that electoral rules facilitated party dominance through two mechanisms: electoral rules disproportionately rewarded existing majorities and, at the same time, discouraged potential majorities from forming. More specifically, the rules rewarded parties that could win a majority of the vote in single-member districts; but at the same time, rewarded minority parties with seats from multi-member districts, mitigating Duvergerian incentives to coordinate behind a single challenger. In the short run, seats from multi-member districts benefited opposition parties by significantly reducing entry costs; in the long run, however, these seats helped sustain party dominance, by discouraging coordination among opposition parties and voters.