When pivotal politics meets partisan politics

Recent years have witnessed many efforts to understand legislative productivity and gridlock. However, despite theoretical and empirical contributions to how preferences and institutions shape political gridlock's level (e.g., Krehbiel 1996,1998) and empirical evidence about how parties may affect political gridlock (e.g., Binder 1999; Coleman 1999), we lack a comprehensive perspective theoretically and empirically examining preferences, institutions, and parties. We overcome this deficiency by modeling conditions for gridlock as a function of preferences and institutions-incorporating bicameralism and presidential influence-and of parties. By generating equilibrium gridlock intervals for empirical testing using Poole's (1998) common space scores, and showing that gridlock intervals associated with models in which parties have no effect or an agenda-setting role do not explain policy gridlock but that those linked to models with party-unity effects and strong presidential leadership do, we demonstrate the importance of accounting for party and leadership roles in explaining legislative choices.