Thae Yong Ho — the most high profile North Korean defector in two decades — told NBC News’ Lester Holt that dictator Kim Jong Un is ‘desperate’ to maintain his rule. Once Kim perceives ‘an imminent threat from America, then he would use his nuclear weapons,’ added Thae, who was living in London and serving as North Korea’s deputy ambassador to the United Kingdom when he and his family defected to South Korea. Watch the full report tonight on Nightly News with Lester Holt.