To explain patterns of political dynamics, this paper develops a model of the circulation of power and compares it with an alternative model, the institutionalization of power, in an event history analysis of CEO succession. The circulation of power emphasizes the internal contests for control and opposition to the CEO that emerge with increased executive tenure and under conditions of economic adversity. The study finds support for an increasing rate of CEO succession during the first decade of tenure, consistent with the model of circulation, followed by a slow decline afterward, consistent with institutionalization. The effects of economic adversity were found to trigger circulation when combined with long prior board tenure and large board size. Also, contrary to conventional views, under economic adversity, more inside board members increase CEO succession.