The authors formulate a model to explain why the lack of political competition may stifle economic performance and use the United States as a testing ground for the models predictions, exploiting the 1965 Voting Rights Act which helped break the near monpoly on political power of the Democrats in southern states.
Link
http://econpapers.repec.org/scripts/redir.pl?u=http%3A%2F%2Fepub.ub.uni-muenchen.de%2Farchive%2F00000769%2F01%2Fpolitical_competition.pdf;h=repec:lmu:muenec:769