Endogenous institutional change in the Mexican senate

This article studies the endogenous transformation of the Mexican Senate. Changes in the electoral rules for the Senate composition are explained as an effort by the Partido Revolucionario Institucional (PRI) politicians to protect their majority in a broader strategy of division and cooptation of its opponents. That strategy expanded seats for the opposition while reducing risks for the incumbent party. The article calculates, through Monte Carlo simulations, counterfactual scenarios for the composition of the Mexican Senate under alternative electoral rules. Those simulations highlight the inherent uncertainty involved in institutional design. In spite of the demise of the PRI in the 2000 presidential election, the Senate will afford in the foreseeable future veto power to the hitherto hegemonic party.