Secretary of State Tillerson explained  the administration’s thinking, such as it is, for imposing additional sanctions on North Korea:
Tillerson cited other recent sanctions from the United States and the United Nations on the North and added that the redesignation “continues to tighten the pressure on the Kim regime, all with an intention to have him to understand, ‘This is just going to get worse until you’re ready to come and talk.'”
No one would accuse the Trump administration of understanding the first thing about diplomacy, but even for them this is a bizarre position to take. Administration officials fail to imagine how the North Korean leadership will perceive and react to these moves. If they gave this much thought, they would realize that Kim is much more likely to view these punitive measures as a challenge, and that would make him even less likely to agree to talks of any kind. The U.S. and its allies have been trying punitive measures for more than a decade without success, and yet they keep clinging to the idea that one of the world’s most isolated regimes can somehow be caused enough economic pain to make it give up on the things that it considers essential to its survival. The U.S. remains wedded to pursuing an unachievable goal (denuclearization) through ineffective means (more and more sanctions), and in so doing it is closing off the one path that might lead to a workable, negotiated compromise.