Trump has already achieved plenty domestically (tax bill, successful supreme court appointment, disrupting regulation efforts at the EPA and FCC etc) but I can't say I see much evidence that this development can be attributed to Trump. Of course, nothing happens on the geopolitical stage without some influence from the U.S, but the evidence I do see suggests that this is mostly a combination of factors having to do with South Korean leadership and other recent positive developments between SK and NK during the Olympics. If it comes out that Trump had a specific role in these negotiations then I think he deserves recognition for that, but as of now I haven't seen any indication of that.