All of this has left many Americans feeling disoriented, their faith that their nation has something distinctive to offer the world shaken. On the left, many have gravitated toward a strange sort of universalism, focusing on America’s flaws while admiring other nations’ virtues. They decry nationalism and covet open borders, imagining a world in which ideas can prevail without nations to champion them.

Even as the left is made queasy by the notion that an idea can be both good and distinctively American, many on the right now doubt that America is a land defined by a distinctive idea at all. President Donald Trump’s rhetoric is curiously devoid of references to a common civic creed. He promotes instead a more generic nationalism—one defined, like any nation’s, by culture and borders and narrow interests and enemies.

Both of these visions are corrosive, although not equally.