Stephen Sackur speaks to the American diplomat Christopher Hill who has served under three US Presidents and was a former lead negotiator on North Korea. Recently, President Trump has described North Korea\u2019s leader Kim Jong-un as a \u201cpretty smart cookie\u201d who he would be \u201chonoured\u201d to meet. But with military tensions on the peninsula rising, could Trump's unpredictable approach to foreign policy actually work?