Party System Change and Abortion Policy: The case of MORENA in Mexico

How does party system change affect abortion policy reform? Existing studies on doctrinal or moral gender policy focus primarily on party ideology. Conversely, research on party system change rarely focuses on gender equality policy. Combining insights from both fields of study, this paper advances a framework that focuses on the entrance of a new party and the potential for change. More specifically, it zooms in on the characteristics of the new party—policy positions, broader ideology, and relationship to major stakeholders in abortion reform such as the Catholic Church—and how its entry alters legislative dynamics among the parties that operate within a given system. Empirically, the paper draws on the emergence of the National Regeneration Movement party (MORENA) in Mexico. Founded in 2014, the party rapidly rose to power in 2018, profoundly altering the party system that was among one of the most stable in Latin America. MORENA’s ascendance ushered in abortion decriminalizations in some subnational entities long before the Supreme Court decision of 2023, yet the party did not pursue such reforms across all its territories. Using a mixed-methods approach, the paper traces abortion politics at the subnational prior to and during MORENA’s rule, highlighting the factors that impacted change, and zooms in on a detailed study of two states where the party held a majority of seats. By examining how new party entrance shapes the prospects of policy reform, the paper contributes to the study of abortion policy and broader institutional change in Latin America and beyond.