Trump and his advisers have repeatedly insisted that the U.S. president can pretty much do whatever he wants and that the pesky Congress need only be consulted rarely.
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?