"However, it is not clear what there is to negotiate."
NK is a surrogate for Beijing.
Beijing is using Kim to bully Trump into backing out of doing Anything about the TPP or doing anything else to staunch the flow of our money into the Chi-Com Party and Chi-Com Military's accounts.
We never should have been trading with China in the 1st place.
So, yes, there really is 'nothing' to negotiate.
China must be cut off, but we'll weasel our way around it, just like O'care, Tax Reform, etc. rather than do the right thing because it's the hard thing to do.