The world economy continues to be thought of like the World Cup: cosmopolitan and transnational, yet made up of discretenational teams competing for a single prize.

As Paul Krugman has pointed out, Mr. Trump’s Democratic predecessors were no exceptions: Bill Clinton, the arch globalizer, spoke of each nation as being “like a big corporation competing in the global marketplace.” Two years into his presidency, Barack Obama relaunched his Economic Recovery Advisory Board as the President’s Council on Jobs and Competitiveness, boldly announcing, “We can outcompete any other nation on earth.”

Angela Merkel’s Germany, supposedly the last great anchor of the liberal world order, is hopelessly addicted to national competitiveness talk. Berlin measures the success of its economic policy not in terms of domestic investment or domestic well-being, but above all in the scale of its trade surplus.

Nor is it merely a German obsession. Competitiveness is an endlessly repeated mantra of the European Commission. Mr. Tusk tweets about it all the time.

So what then is so upsetting about Mr. Trump’s latest outburst?

One of the president’s favorite taboo-breaking moves is that he likes to name enemies, especially those hiding in what is supposed to be America’s own camp. In doing so, he not only offends Atlanticist decorum but also violates a more specific injunction, which permits politicians to talk as much as they like about global competition but not about specific competitors. Normal talk about globalization and competitiveness is directed inward, to the nation. It serves as a call to discipline and hard work. Mr. Trump is taking the idea and pointing it outward, calling out his supposed foes. In so doing, he deliberately fosters economic nationalism.

Conventional competitiveness rhetoric treads a fine line. The point is to stir the pot without causing things to bubble over. With Davos types like Ms. Merkel, you know that whatever rhetoric they employ in public, there are people working behind the scenes who respect international law and global treaties, who understand that blatant national favoritism will blow the system up. The same cannot be said for the Trump administration, which has actually imposed tariffs. They are modest so far, but Mr. Trump has a relish for escalation.

And this evokes an even deeper fear. It is one thing to indulge in competitiveness talk in a world fundamentally headed toward integration. But Mr. Trump speaks this way in a world in which the direction of travel is profoundly uncertain.