What makes Europeans particularly vulnerable in the Trump era is that they view themselves as America’s allies. (That’s for good reason: They have been, after all, America’s allies for the past 70 years.) But in Mr. Trump’s world, there no longer is any concept of alliances. It is not that he is displeased with European military spending or with Europe’s position on Iran. Rather, it is that in a world where America is a disrupter and not a force for stability, allies are now a burden. They have expectations and claims that constrain America’s policies, whether that is a preferential trade agreement or a commitment to joint military exercises. Worse, they insist on predictability and reciprocity, which are completely out of sync with Mr. Trump’s view of the world.

Peering through Mr. Trump’s twisted prism, one finds not friends and enemies, but fans and enemies. Fans are those who are loyal to you no matter what; they never expect reciprocity. Enemies are also valuable because they help you solve problems; you can assert your power by breaking them or befriending them. The Trump administration’s approach to the North Korean enemy is a perfect example of this. Its relationship with Russia — Mr. Trump is meeting with Vladimir Putin next week — could be the next example.