The South Koreans government has petitioned the US Government for decades to provide it with nuclear weapons to protect it from North Korea. Those pleas have always been rejected and the US assured their friend and ally, South Korea, that the American nuclear arsenal stood ready to assist. There were US presidents who could be trusted to act, but the North Koreans don't seem to be much impressed with Obama. No, nobody else seems to be either.
In order to allow South Korea the freedom to act in their own defense so that the US President doesn't have to do that --- and can disavow whatever they do, maybe it's time for us to provide them with two or three dozen tactical nuclear weapons and cruise missile (and/or other) delivery systems? What about it, Barack?