Trump does not deserve credit
Giving Trump credit for NK wanting to talk is ridiculous. They want to talk because their nuclear program has reached a successful completion. They've demonstrated nukes, a hydrogen bomb, and missiles able to reach the US. They have nothing to prove by further tests, since the only thing they haven't demonstrated is the ability to deliver a nuke on an ICBM which they can't do for obvious reasons. Their H-bomb test supposedly caused significant damage to their test site, so it is easy for them to make themselves look good by saying they will decommission it "as a sign of good faith".
After they expended so much effort developing nuclear weapons and the means to deliver them, they aren't going to "denuclearize". They might claim they will, but with such a closed off country we know so little about internally, it would be easy for them to have long ago hidden a few nukes, international inspectors can only look in places they know to look, and they wouldn't know where to find them. NK has previously made "deals' before they haven't kept, only a fool would take them at their word that will denuclearize.
What they really want is for sanctions to be lifted, so they will agree to decommission their useless test site, hand over / destroy their centrifuges, allow international inspectors to check their reactor(s) to insure they aren't generating high grade uranium that can be refined to weapons grade, etc. They will hand over a few nukes and missiles, claim that's it, but it won't be. They would never give up everything, even in exchange for the US pulling all troops from SK (which we might agree to but will have such a long timetable it will never actually happen)
Anyway, why would they trust the US to keep a deal after Trump tore up the Iran deal? There's zero guarantee that the next president wouldn't decide Trump made a bad deal with NK if he agreed to remove all troops, and reverse that order.