Prior to joining CFR, he worked at the Harvard Kennedy School , Brookings Institution, Congressional Research Service, and the State Department's Office of Policy Planning. He writes the CFR.org blog “Politics, Power, and Preventive Action”, which covers U.S. national security policy, international security, and conflict prevention. He is the author of the book, Between Threats and War: U.S. Discrete Military Operations in the Post–Cold War World. He is the author of two Council Special Reports, Enhancing U.S. Preventive Action, with CPA director Paul Stares, and Toward Deeper Reductions in U.S. and Russian Nuclear Weapons, which was published in November 2010.