This paper examines how partisanship influences the willingness of an overseer to exercise her check on executive power. In doing so, we provide a theory of divided government based on the need for effective oversight. The sequential nature of oversight means that by the time the overseer is called upon to act - either to accept or veto an executive initiative - it has already been revealed what the executive believes should be done. This information can then lead a career-minded overseer to distort her behavior in order to protect her reputation. Our main result is that partisanship can mitigate such inefficiencies, as the distortions caused by a partisan overseer's desire to affect the executive's reputation can offset the distortions caused by her desire to enhance her own.