Oh noes! North Korea is building missiles to launch one at us! Yeah, don't be stupid. Missiles are costly and take a ramp up to deploy over years and many tests. There is no threat from North Korea or any other developing nation concerning missiles that won't be seen years in advance.
The actual threat is not missiles, but nuclear weapons themselves. Smuggled in in a shipping container or in the boot of a car. You think it is any accident that people getting radiation treatment for cancer are, fact, setting off radiation detectors as they drive down highways and then getting stopped and searched? The USA is already ahead of the real threat, smuggled warheads, talk of North Korea or other fanatics building missiles just makes good TV for the masses.