A 1960 accord with Japan permits the United States to move weapons of mass destruction through Japanese territory and allows American warships and submarines to carry nuclear weapons into Japan's ports and American aircraft to bring them in during landings.
Any nuclear attack on Japan therefore is sure to be a nuclear attack on the United States and would trigger massive American nuclear retaliation. Thus these recent threats are as much a nuclear strike threat against the United States as Japan, and there is no doubt at all the Japanese understand this well.
