It was only natural that the egomaniac-in-chief in the White House would see no need to get his allies on board with the campaign, not even diplomatically.
With his reliance on naked power and rejection of all constraints on his authority, Trump represents the opposite of everything that made the U.S. great.
If boat trips from a few hundred years ago are not a claim of ownership, then why should this just apply for Denmark in Greenland, and not also for the European colonizers in North America?