U.S. President Donald Trump’s fixation on Greenland offers an ice-cold reminder to leaders in Europe and abroad: No deal is ever final.

Trump announced a 10% tariff, rising to 25% in June, on eight European nations, including Denmark, for saying they would undertake token NATO military exercises in Greenland in response to U.S. saber-rattling.

While the tariffs aren’t certain to take effect, the threat was a brazen escalation and insult to close U.S. allies, trampling over the U.S.-EU trade deal reached only six months earlier at Trump’s Turnberry resort in Scotland.