He specializes in political philosophy, the philosophy of law, and the history of legal and political philosophy. His current research focuses on popular sovereignty and constitutionalism, the thought of Hans Kelsen and Carl Schmitt, and early modern political philosophy. He is the author of two books, which have been published at Oxford and Cambridge University Press, and of numerous articles, which appeared in Political Theory, the International Journal of Constitutional Law, and the Canadian Journal of Law and Jurisprudence, among others.