Insurmountable security concerns for President Trump?
Maybe later then, in his last year as President if he is re-elected to second term. Let Japan and Taiwan go first and leave intact.
Correct, the Secret Service and US Military would needs a couple of weeks to do intel on the area where the summit would be held. There would be no way NK would allow things like manholes being welded shut, F-15s flying overhead, snipers on rooftops etc.