Why a clean politician supports dirty politics: A game-theoretical explanation for the persistence of political corruption

► I show that when political competition is among a small set of career politicians with no term limits, political corruption produces a positive externality for the clean politician as well. ► Studying an infinitely repeated political duopoly, I identify the set of parameters under each politicians promises are credible, and then the subset under which neither politician promises the reform in a Nash Equilibrium. ► Compared to a (legal) rent-maximizer, a policy-motivated politician has stronger incentives to adopt the reform when the level of corruption is low; but, when the level of corruption is high, he too, will choose not to adopt the reform when the corrupt one did not adopt it.