This paper expands the theory of veto players into the realm of presidential
regimes. We bridge two strands in the study of comparative institutions: the work on veto
players in parliamentary systems (Tsebelis 1999; Tsebelis 2002) and the analysis of
executive-legislative relations under presidentialism (Mainwaring and Shugart 1997b;
Shugart and Carey 1992). Early studies of veto players in presidential systems
(Cameron 2000; Krehbiel 1998) have not always shared the same theoretical
assumptions or even the same language used by students of parliamentarism, and only
recently some systematic attempts to bridge this gap have taken place (Alemán and
Tsebelis 2002; Ames 2001). At the same time, a burgeoning comparative literature on
presidential institutions has generated important conclusions about policy stability and
policy change, many times borrowing (but not always formalizing) the assumptions of
the veto-player theory.
In the first part of the paper we introduce the basic concepts and outline the setup
for the analysis. In the following sections we develop a series of systematic hypotheses
about presidential systems. Section two explores the relationship between the legislative
powers of the president and the configuration of veto players in presidential regimes.
Section three discusses how the number of legislative parties and their internal cohesion
affect policy stability. In the fourth section, we develop a computational model to
estimate the impact of these factors in our two-dimensional model of policy stability.
The simulation suggests that decree authority is a key factor affecting policy stability in
presidential regimes, and that the impact of most institutional variables is conditional on
the spatial location of the key players.
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Convention