If such an attack did take place the U.S. response would be a sternly worded letter followed by an apology to N. Korea.
Seem to be the status quo, doesn’t it....
Curiously that is what happened when the North Koreans torpedoed a South Korean warship. However I wouldn't necessarily bet on that outcome. Remember, this is the President who has left 100,000 American troops in Afghanistan after announcing the date of our surrender. He's bombed Libya into regime change because the UN ordered NATO to get the oil flowing again. He's sent hundreds of American troops into places they have no business such as Nigeria, Central African Republic, Jordan, Pakistan and Egypt. He's bombed countries with planes and drones from Pakistan to Yemen to Somalia to Mali.
Democrats are a lot of things but they are seldom scared of putting our forces in harms way for dubious reasons. It's the one and only thing I'll give Jimmy Carter credit for. He wasn't into nation building.