I'm sure you know about THAAD right? The anti-missile defenses currently set up in South Korea? Its used to detect nuclear launches against Japan and South Korea and prevent them by sending counter missiles to intercept, i highly doubt that any missiles would come anywhere near America let alone get out of North Korea before being shot down by either the THAAD or the fleet of American warships that have arrived off of the North Korean coast or Us and Japanese air forces located on the Aircraft carriers in the fleet. The North Koreans know that setting of a nuke will be the end of them, if they didn't they would of all ready done it, and with allies rushing to America's side, North Korean allies are beginning to give up, i wouldn't worry about an attack, they haven't even prove that their main documented missiles can reach Washington yet, let alone out of Asia.