In a face-to-face meeting, President Obama warned his successor that America’s biggest security concern was North Korea. Since then, Pyongyang has conducted a series of ballistic missile tests, countered by a successful anti-missile test from Washington. Robert Gallucci, the chief U.S. negotiator during the last major crisis over North Korea’s nuclear-weapons program, talks with David Remnick about the value of deterrence and engagement. He notes a lack of coherence in the Trump Administration’s statements on North Korea, which seesaw between overtures toward negotiation and warnings of possible war. With leaders in each country who are “known to be impulsive,” Gallucci doesn’t see an easy resolution to the crisis.