This willingness to equate American white supremacy with the barbarism that occurs in other countries has also shaped the way the left describes “terrorism.” In past decades, the term was reserved almost exclusively for America’s enemies, particularly in the Muslim world. Now it’s become common, not only among leftist commentators but among Democratic politicians, to apply the term to violence committed by native-born white Americans. “America’s greatest terrorist threat?” asked New Jersey Congressman Tom Malinowski in an op-ed last month. “White supremacists.”

Ocasio-Cortez’s comment about “concentration camps” is only the latest example of this broad challenge to American exceptionalism. She didn’t claim that Trump’s detention centers are the equivalent of Auschwitz. But she denied that America is a separate moral category, so inherently different from the world’s worst regimes that it requires a separate language. On Tuesday night she retweeted the actor George Takei, who wrote, “I know what concentration camps are. I was inside two of them, in America.” This was another act of linguistic transgression. When remembering the detention of Japanese-Americans during World War II, Americans have generally employed the term “internment camps”—largely, the historian Roger Daniels has argued, to create a clear separation between America’s misdeeds and those of its hated foes.

It’s that separation that Ocasio-Cortez and others on the Millennial-led left are challenging now. They are challenging not only the physical and legal barriers that Trump is erecting against immigrants entering the United States but also the conceptual barriers that American exceptionalism erects against seeing the United States as a nation capable of evil.