The US is facing the risk of N. Korea developing it's own nulcear Inter Contenential Basslistic misscles (ICBM). Although the US has the largest nuclear arsenal, and imposes many trade sanctions on N. Korea; the N. Koreans still has the capaxity to destroy the USA's allies Japan and S. Korea. Their support can be demonstrated by the thousands of troop in allied countries. Although N. Korea has the nuclear warheads the ICBM technonlgy is not yet complete as they are in phase 3/4 in development.
Also the POTUS's remark on N. Korea could potentialy risk the US's careful balance on N. Korea.
I hoped that helped and if you want a super professional, easy to watch vid I'd consider watching VOX's "The North Korean Nuclear Threat, Explained" on YouTube
