The American public has short memories, does not know a thing about Japan's ugly history in WWII other than Pearl Harbour, and can be easily goaded into war fever based on the flimsiest pretexts (how many times have I mentioned Iraq and you never seem to noticed?). I gurantee you 99.99% of the US public has never heard of either the Cairo or Potsdam Declarations. US foreign policy can change in a moment, again look at Saddam Hussein and Kuwait.
If the US is sufficiently desperate and intent on eliminating China as a potential rival, then some might consider it worthwhile losing Korean support. The small Asian countries don't even matter.
As for nukes, how many does the US have compared to China? That's more massacre than MAD.