Political Opposition, Legislative Oversight, and the Performance of the Executive Branch

The separation of powers between the executive and legislative branches is a cornerstone of democracy. This system of checks and balances, however, can be circumvented by partisan loyalties if legislators strategically avoid exerting oversight when their own party controls the executive branch. It is thus an empirical question whether the separation of powers prevents the abuse of power in practice. We answer this question by measuring the extent to which members of political opposition parties in a city council effectively check the mayor's performance in Brazil. We employ a regression discontinuity design to estimate the causal effect of an additional politically opposed legislator, and we find that political opposition increases oversight action and decreases corruption, with the effect fully concentrated on mayors facing reelection pressure. We trace the impact of oversight, via a reduction in healthcare spending irregularities, all the way to impacts on healthcare service delivery and health outcomes.