If a summit between Donald Trump and Kim Jong-un really takes place in May, it will count as one of the most remarkable and unexpected pieces of theatre in diplomatic history. If that drama leads to a substantive peace agreement it would represent an extraordinary achievement. The Korean war never formally ended and the threat of a new devastating conflict has hung over the peninsula for decades. It is a prize on an epic scale, but so are the risks. Both leaders view the provisional agreement to meet as a personal triumph born of resolve. If each reckons he has the other over a barrel, they will be little room for compromise if and when they meet.
