"Hit" implies that they have a delivery system that is related to the old triad (Bombers, ICBM, SLICBM). For a state such as NK to deliver an atomic (not nuclear, they have not demonstrated anything approaching thermonuclear capability), I would think that since they do not have a typical delivery system, that they would consider an atypical method that wouldn't require ballistic missile tech, cruise missile tech, intercontinental bombers or submarines. They don't have a reliable delivery system and they don't have miniaturization technology approaching that of long-term "club members" that would allow them to make a small enough (yet powerful enough) device that could reach our targets. They are most likely at the stage where their devices are of the size, weight and technology of Fat Man and Little Boy but have no way to get them from there to here. So, put it in a lead lined cargo container, ship it all over (like playing a shell game) and eventually have it arrive in a port or airport, or on a train or a truck that puts the container and device in whatever city they want. Then a phone call to the cell-phone attached to the detonator..... and we've got a mushroom cloud in ANY city on the planet. It's low tech, but cheap and feasible. We didn't think of airliners as flying bombs until 2001 and I suspect that most nations don't see cargo containers as rolling bombs until someone uses them as such (well, they have, we've just not paid too close of attention). Multiple embassy/compound bombings and Oklahoma City should remind us of what a truck with fertilizer/fuel oil can do. Imagine something the yield of Hiroshima or Nagasaki on a train, or a semi, or stacked in the container yard of a port. Scary to you? It scares the everloving crap out of me. As to our response? If you think that the US's reflexive and emotional reaction to 3 buildings and 3,000 deaths in the years after 2001 was mindless, overwhelming and deadly? I would imagine that if there was a mushroom cloud over where a US city used to be, that the country would be screaming for blood and vengeance, not calm and rational response. I could easily see the President (yes, even this one) simply go on television and tell the rest of the world "Sorry guys, but we know who's been making these threats, stay out of this, we're going to deal with it. Oh, and if you're a non-hostile nation in and around the Korean peninsula? Do yourself a favor and duck!"