For nearly 30 years, through the five presidential years, the United States has not stopped the Korean weapons program.
Obviously because China has been supporting NK. But that is changing.
The only reason why China has been supporting the DPRK is because they don't want any American military bases right there on the border (like they have in South Korea and Japan). But now, they have reduced a lot of support services which they used to provide to the DPRK. It seems that Russia has replaced China as DPRK's main supporter.