While the role of interest groups' contributions in shaping policies has been well-studied, little is known about their effects on political competition and selection. This paper exploits a Brazilian reform that banned campaign contributions made by firms. I compare a range of political outcomes across municipalities and individuals according to their degree of dependence on interest groups' contributions prior to the reform. I find that the reform encourages the entry of new candidates and deteriorates the incumbency advantage. Those effects favor insider challengers, especially the ones from major parties.