For the first time as US President, Donald Trump will be in Kim Jong Un's immediate neighborhood.

The US President landed in South Korea on Tuesday, his second stop in Asia on a nearly two week-long trip, where the standoff with North Korea is likely to loom large.

The threat posed by North Korea's development of nuclear weapons and long-range missiles has been a top foreign policy priority for the Trump administration. The worry is that should Pyongyang successfully pair the two technologies, the reclusive country would have the potential to launch a devastating strike against a US city.