As Barack Obama scanned the North Korean landscape through his binoculars on Sunday, the US president could at least feel reassured that America and its spy satellites have a rough idea where that particular enemy is.
But he faces more elusive foes in a summit in Seoul on Monday and Tuesday. He will have to press world leaders to combat the threat of terrorists getting fissile material from a shadowy nuclear bazaar that stretches over some of the most lawless parts of the world.
Immediately after arriving in South Korea, Mr Obama headed to the world’s most militarised border to peer over the sand bags and barbed wire into Kim Jong-eun’s closed state. “You guys are at freedom’s frontier,” he said to the US troops guarding the border.