North Korea has apparently conducted an underground nuclear test earlier today. The incident registered as a 5.1 magnitude earthquake. North Korea claims the test was of a Hydrogen Bomb, as opposed to a lower yield Atomic Bomb. South Korean spies claim it was of the latter type.
Regardless, the test drew international condemnation, including from that of their benefactor/protector, China. The U.S. joined in the condemnation.
I would expect no further action from the United States. The president is focused far too keenly on his next domestic agenda item, gun control. He also has a history of excessive softness on foreign policy; with Russia, with China, with Syria, multiple instances with Iran, with Venezuela and previously with North Korea. He's soft and the international perception is that he is ineffectual in projecting American influence.
In other words, he's not going to do anything, and the world is currently an unpoliced Wild West where you can do anything you want without consequences. For example, you can conduct a test of an underground nuclear detonation and get not even a slap on the wrist but rather the geopolitical equivalent of rolling eyes.