Former Georgia Democratic Sen. Sam Nunn has spent years studying the threat of nuclear expansion.  He is the co-founder (with Ted Turner) of the Nuclear Threat Initiative and a distinguished professor in the Sam Nunn School of International Affairs at Georgia Tech.  

During his years in the Senate, he chaired the Armed Services Committee. In a conversation with Denis O'Hayer on "Morning Edition," Nunn discussed the dangers North Korea's nuclear capability pose to its neighbors -- and some less obvious but equally troubling threats.