One problem with Trump’s style of negotiation, is that he is so mercurial, he could work out a trade deal on one set of presumptions, and then undo it because of something completely unrelated (e.g. annexation of Greenland). It is hard to plan around that. While treaties are broken more often than not, the speed at which Trump does it may not sit well in an unstable situation where EVERYTHING is at stake . That works better with the European powers, who SHOULD care about their own economies more than who is the sovereign of Greenland. They might not do the practical thing, if they think their own credibility or legitimacy is at stake.
A good point. While Trump gets flak for proposing outrageous things, the bigger problem is that tomorrow he’s just as likely to say exactly the opposite.