For the past 70 years, the nations of the world have more or less agreed that the role of nuclear weapons is to discourage aggression: owning them is one thing, but using them is beyond the pale. Now, two volatile world leaders with considerable nuclear arsenals at their fingertips are engaging in bellicose rhetoric. How nervous should we be as we read the threatening tweets coming out of Washington and Pyongyang? Nina Tannenwald is a faculty fellow at Brown University's Watson Institute and director of its International Relations program. She writes often on issues of nuclear proliferation and her book, The Nuclear Taboo: The United States and the Nonuse of Nuclear Weapons Since 1945 won the 2009 Lepgold Prize for best book in international relations. You can read a transcript of this episode here: [https://drive.google.com/file/d/1mvR8T31cTGf_pJaSfyOwQOAduMGKFASV/view?usp=sharing]