How One Party Controls the Agenda Without a Majority in Mexico's Fragmented Congress

🧭 Main Argument

This essay develops a theory of strategic legislative agenda control showing that a single party can effectively set the agenda under majoritarian gatekeeping rules without holding a majority—or even a plurality—of seats. The agenda-setting party need not be the median party in the assembly and does not require support from executive-led parliamentary coalitions to do so.

📍 Where This Happens: Mexico's Chamber of Deputies

The Mexican Chamber of Deputies serves as the case study illustrating how institutional rules and political context create conditions for one-party-led agenda-setting in a fragmented congress. The Partido Revolucionario Institucional (PRI) demonstrates that the failure of opposition coalitions to roll the PRI reflects the party's ability to set the agenda through strategic coalition formation since 2000.

📊 How Evidence Was Assembled

• Roll-call data analysis underpins the argument.
• Voting and preference measures include WNOMINATE and WRice scores.
• Roll rates are used to document coalition behavior and agenda outcomes.

🔑 Key Findings

• Majoritarian gatekeeping rules can enable agenda control by a single party even when that party lacks majority or plurality status.
• The agenda-setter need not be the median party nor dependent on executive-led coalitions.
• High levels of party unity combined with strategic positioning allowed the PRI to steer the legislative agenda in the Chamber of Deputies.
• The PRI's coalition-making is strategic and consistent with a historically pragmatic approach to forming alliances; this behavior is documented in roll-call patterns and roll rates since 2000.

📌 Why It Matters

This argument reframes expectations about who can control legislative agendas in fragmented parliaments: institutional gatekeeping and strategic coalition formation can substitute for numerical dominance. The findings have implications for theories of agenda-setting, coalition politics, and how legislative institutions shape power in multiparty systems.