The United States have deployed an aircraft that specializes in detecting nuclear fallout to the Korean peninsula, leading many to predict that they are expecting a possible nuclear attack from North Korea. The WC-135 Constant Phoenix, known colloquially as a 'nuke sniffer' was dispatched to the Kadena Air Base in Okinawa Prefecture, Japan over the weekend amidst rising tension between the U.S and North Korea.
Missile and nuclear testing from North Korea and the deployment of troops and recourses from the United States close to the North Korean border have increased tension in the are over recent months. The most recent development being Kim Jong Un's threat to turn the sky between the North and Sout into a 'sea of fire'. In other words a thinly veiled threat to fire North Korea's extensive artillery batteries at the South and the American bases situated there.
At this stage, the actions of either side are seemingly aimed towards eliciting a reaction from the other. Should this progress further, however, all out war could be a possibility. North Korean leader Kim Jong Un's predecessor, his father Kim Jong Il, seemed to be aware of the precarious position he was in, despite his similarly provocative actions towards the west and South Korea with his missile tests and inflammatory statements. Kim Jong Un, however, is seemingly more reckless and is likely taking the actions of this grandfather further as a show of strength.
The American presidents for the majority of Kim Jong Il's rule were aware of the fact that there was little chance of the self-styled supreme leader of ever actually attacking either the United States or South Korea. Current president Donald Trump, however, has thus far been adopting a much more hard-line approach with North Korea. Aside from preparing for possible conflict by moving troops and resources to the peninsula, he has also urged China to distance themselves from the hermit nation, which they seem to be doing, with a recent ban on coal imports from North Korea, a substantial portion of their total exports.
The presence of the aircraft would outwardly suggest that the United States is preparing for the possibility that North Korea might try to use nuclear weapons of some kind. Whether this is actually very likely is another matter, with most experts predicting that any conflict to come will not involve nuclear weapons.
Despite their missile tests and provocative shows of force, the reality is that North Korea's nuclear capabilities aren't as dangerous as the media tends to portray. In terms of technology, military budget, delivery systems, military intelligence and numerous other metrics, North Korea are decades behind both the United States and South Korea. They are also slowly losing the backing of China, their only real ally.