In 2017-2018 he was a senior advisor to the Secretary of State in the Office of Policy Planning working on European affairs. Previously, he was a Senior Fellow at the Center for European Policy Analysis and on the faculty of SAIS-Johns Hopkins University in Washington DC. He is the author of Return of the Barbarians (Cambridge University Press, 2018), Great Powers and Geopolitical Change (JHU Press, 2006), and co-author with Wess Mitchell of The Unquiet Frontier (Princeton University Press, 2016). His writings on international relations and security studies have appeared in Foreign Affairs, The American Interest, Security Studies, Journal of Strategic Studies, Orbis, Commentary, Parameters, as well as several U.S. and foreign newspapers. He earned a Ph.D., M.A. and an MPA from Princeton University, and a BSFS Summa Cum Laude from Georgetown University.