this paper develops a computational model to explore the effect of veto players in presidential regimes.We discuss the relationship between the legislative powers of the president and the configuration of veto players, and analyze how the number of legislative parties and their cohesion affect policy stability.We develop a computational model to estimate the simultaneous impact of these factors in a conventional twodimensional policy space.the results suggest that party fragmentation has mixed implications while decree authority is a key factor explaining policy stability.the impact of most institutional variables is conditional on the position of the players.