When and how do democratic institutions deliver accountable government? In addressing this broad question, we focus on the role played by political norms—specifically, the extent to which leaders abuse office for personal gain and the extent to which citizens punish such transgressions. We show how qualitatively distinct political norms can coexist because of a dynamic complementarity, in which citizens’ willingness to punish transgressions is raised when they expect such punishments to be used in the future. We seek to understand the emergence of accountability by analysing transitions between norms. To do so, we extend the analysis to include the possibility that, at certain times, a segment of voters are (behaviorally) intolerant of transgressions. Our mechanism highlights the role of leaders, offering an account of how their actions can instigate enduring change, within a fixed set of formal institutions, by disrupting prevailing political norms. We show how such changes do not depend on “sun spots” to trigger coordination, and are asymmetric in effect—a series of good leaders can (and eventually will) improve norms, whereas bad leaders cannot damage them.