If the U.S. Congress had its civic act together instead of being as corruptly partisan as it actually is, it would pass a bill stating that, as far as the USA is concerned, the Korean War is over and the U.S. is withdrawing its military and every single nuclear weapon it currently has in South Korea, while instructing South Korea to return every nuclear weapon of America's in its possession to American possession.
End the Korean War.
Remove all U.S. military personel from South Korea.
Denuclearize South Korea.
Give Kim Jong-un exactly what he says he needs to denuclearize North Korea by removing any excuse of American attack and takeover as the alleged reason for his nuclear missile ambitions. Pave a golden way for the South and North to continue to reconcile as they wish, not as the U.S. expects.
The U.S. Congress has full constitutional power to do all this by simply putting a bill on President Trump's desk to enact. They should step up to the Good for America plate and just do it.