1. University of California-San Diego, 9500 Gilman Dr., San Diego, CA 92093, and NBER.
2. Center for International Security and Cooperation (CISAC), Stanford University, 616 Serra St., Stanford, CA 94305.
3. Woodrow Wilson School, Princeton University, Princeton, NJ 08544.
4. University of California-San Diego, 9500 Gilman Dr., San Diego, CA 92093.