Electoral Rules and the Size of the Prize: How Political Institutions Shape Presidential Party Systems

This paper explores how political institutions besides electoral rules shape the presidential party system. Our focus is upon what we call the “size of the presidential prize”: the degree to which authority is concentrated in the presidency vis-à-vis the legislature (horizontal centralization) as well as in the national level of government vis-à-vis the subnational levels (vertical centralization). We find a significant but nonlinear relationship between the horizontal centralization of authority in the presidency, operationalized either as an index of presidential powers or as regime type, and the presidential party system, operationalized as the effective number of presidential candidates. Specifically, for moderately powerful presidents, increasing presidential powers leads to fewer presidential candidates; however, for either extremely weak or extremely powerful presidents, increasing presidential powers produces a larger number of candidates. Further, we find that the substantive effect of horizontal centralization is generally larger than the effect of the electoral formula—heretofore the most discussed determinant. Our findings regarding vertical centralization, operationalized either as central government revenue as a percentage of GDP or central government revenue as a percentage of total government revenue, are similar to if weaker than our findings regarding horizontal centralization.