SOURCES: Staff and Wire Reports, Nuclear Threat Initiative, Congressional Research Service, Natural Resources Defense Council, GlobalSecurity.org, Department of Energy, Department of State, U.K. Ministry of Defense, NATO Parliamentary Assembly, Defense Intelligence Agency, Federation of American Scientists, Public Broadcasting Service, Council on Foreign Relations
CREDITS: Design by Adam J Kipple; Research by Heather Farrell; Editing by Amanda Zamora - washingtonpost.com


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