The last time I looked, it was the US bullying the North Koreans with nuclear-armed B-52s & B-2 Stealth bombers.
The us neither confirms nor denies carrying nuclear weapons so you have no idea. Logic tells me that they would not risk carrying them in such areas in case of accident. The nearest nuclear weapons are probably in bunkers on Guam and Okinawa. If they did recommission the SAC they would patrol well out in the Pacific. Any standing patrol wild likely be anti-missile defences and they would not have to go anywhere near N Korea.
The US is entitled to have joint exercises with S Korea.
The North IS a threat because of their huge standing army. It is not expected to still be fighting after a week but with Seoul so close to the DMZ a lot of damage could be done. If they were stupid enough to march south, the nuclear option would be on the table, I believe.
