President Donald Trump is coming to Europe. And not for the first time, he has embarrassed a U.S. ally and reached out to Russia's Vladimir Putin before even boarding a plane.

Trump's abrupt decision to cancel a state visit to Denmark planned for Sept. 2 has sparked outrage in the Scandinavian nation, which although small has been among America's most steadfast military allies, from Afghanistan to Iraq and beyond.

The rationale from the U.S. president for dropping such a grenade into the relationship was startling. Trump said on twitter Wednesday he called off the trip because Prime Minister Mette Frederiksen refused to consider selling Greenland, a Danish autonomous territory in the Arctic. She said it wasn't Denmark's to sell.