Change and continuity in the Mexican party system: the 2018 and 2021 federal elections

We analized a number of dimensions of change in the Mexican party system that occurred in the 2018 and 2021 federal elections, based on aggregate electoral data and public opinion surveys. The Mexican system, once considered as one of the most stable in the region, has undergone a gradual but considerable deinstitutionalization in the past decade. This has become evident by the significant loss of the electoral and legislative strength of parties that had traditionally structured political competition during most of the era of multiparty competition. A large part of this deinstitutionalization is the result of a large-scale process of partisan dealignment that has mainly affected mainstream parties. Decline in partisanship has in turn had important consequences for political competition and the current configuration of the system, fostering growing party fragmentation, electoral competitiveness and volatility.