N Korea considers US troops in and around the peninsula to be a threat, and probably removing these troops is part of Kim’s definition of “denuclearization.”
My guess is that building bridges with N Korea will need to be the project of China, S Korea, Japan, and other countries, without cooperation of the US under Pres Trump.
US troops in SK are there as an automatic trigger for intervention: no president could ignore an invasion that costs US lives.
A withdrawal would make it much easier for a current or future administration to ignore NK aggression.
KJU has made it clear that he won’t give up his nukes, and there is nothing Trump can offer that would make it worth doing so. Bolton mentioned the “Libyan model”, which is the quintessential cautionary tale about NOT giving up any WMDs you might have.