He specializes in political theory and, in particular, normative issues underlying questions of public policy. He is the author of Immigration and the Constraints of Justice (Cambridge, 2011), as well as articles on a wide range of issues, including immigration, campaign finance, and philanthropy. These papers have appeared in a variety of leading journals in political science and philosophy, including Philosophy & Public Affairs, The Journal of Political Philosophy, The Journal of Politics, and Law & Philosophy. He currently serves on the editorial board of The Journal of Political Philosophy.