I don't believe North Korea has the capabilites to launch a TBM at the U.S.A., but rather only at its neighboring Countries. U.S., Russia, Great Britain, France, and Japan (Not sure, maybe China) are the only nations in the world with that capability. Other nations have Nuclear threats, but not very effective means to carry out those threats.

Indeed, that would be a very distressful day/moment in American (or any Nation's) history. Much would change due to that "button being pressed." Much mayhem, chaos, and mass destruction would result, and not many lives would, or even could for that matter, be spared. Lets just hope this hypothetical situation doesn't take place anytime in the near future.