At first, it seemed as if it was just one more example of President Donald Trump trolling his critics. When, following his re-election in 2024, the president revived the idea of the United States acquiring Greenland by one means or another, most of his supporters probably didn’t think he was all that serious about it.

But in recent weeks, as his demands that Denmark sell the Arctic land mass escalated, it became clear that he wasn’t kidding. His threats that America might punish NATO allies with tariffs if they didn’t go along with the scheme or that the United States might even take Greenland by force have turned the question of the ownership of one of the least green places on earth into a foreign-policy crisis.

Rather than just a function of what critics consider his megalomania and instinctive authoritarianism, control of Greenland is an important issue that requires serious examination. More than that, the discussion raises serious questions about not just how to value allies but what the United States has a right to expect from them. This applies not just to U.S. relations with NATO but to what America can expect from Israel, as well as what, in return, Jerusalem should expect from Washington. Meanwhile, NATO countries are wringing their hands and bewailing what they consider to be Trump’s bad behavior.