ABSTRACT
Mexican politics has been dominated by one party and noncompetitive elections since 1929, but the Mexican political system has never been a strictly single-party system. This chapter focuses on one institutional aspect of the process that has enabled the stability: the different electoral systems that—through a permanent process of adaptation—have supported that singular piece of equilibrium, the hegemonic party system. The endurance of Mexico's hegemonic party system results from a constant process of electoral reform that has steered a delicate course between the Scylla of internal factionalism and the Charybdis of the depletion of a loyal opposition. In contrast with other countries, Mexico's electoral formulas have been based on two principles: differentiation and segmentation. Consequently, in 1991 the Partido Revolucionario Institucional (PRI) reformed the electoral law to reinforce the governability clause. Mexico's mixed pattern of reform reflects a process of political adaptation by the government, which "reacts" to short-term pressures from the opposition.
