Leah Millis / Reuters

One of the paradoxes of modern-day American politics is that white identity politics can be a potent political platform, as long as you don’t call it that. Policies with racist effects are often popular; explicit racism is verboten.

Thus Donald Trump can win the presidency while running, as my colleague Adam Serwer documented, on a program of discrimination, but when Corey Stewart, a Republican politician in Virginia, makes his white-identity politics too explicit he gets shunned by the GOP.

Sometimes, however, the president’s mask slips, usually at moments of national crisis, and he says the quiet part loud, as The Simpsons memorably put it. This happened after race riots in Charlottesville, when Trump insisted there were good people among the white-supremacist marchers. And it’s happening again now in the context of separating families at the borders.

After days of insisting, falsely, that the separations were the result of some Democratic-passed law, the president has partially shifted gears, defending the policy in a series of tweets. The most shocking is this one, with its description of unauthorized immigrants as an “infestation”:

In late May, a debate erupted after Trump said, during a roundtable in California, “We have people coming into the country, or trying to come in—and we’re stopping a lot of them—but we’re taking people out of the country. You wouldn’t believe how bad these people are. These aren’t people. These are animals.” The White House said that in context, it was clear that Trump had been referring to members of the gang MS-13. Others argued that given Trump’s previous language about immigrants, he didn’t deserve the benefit of the doubt, or that even if he did, the result of the comments was to dehumanize immigrants.

Trump left himself no such plausible deniability in Tuesday’s tweet. The infestation he refers to isn’t simply illegal immigrants per se, though he mentions the gang as well. Nor is this merely the pious language of enforcing the law, though Trump uses that elsewhere.

“Infest” is the essential, and new, word here. (Also popping up in the tweets is the older coded wordthugs.”) It drives full-throttle toward the dehumanization of immigrants, setting aside legality in favor of a division between a human us and a less-human them. What are infestations? They are takeovers by vermin, rodents, insects. The word is almost exclusively used in this context. What does one do with an infestation? Why, one exterminates it, of course.

If those apprehended are less than human, then Trump can shrug the problem off as “only” 2,000 children separated from their parents, though the Washington Examiner reported Monday that 30,000 children could be held by August. Since Trump has previously said he didn’t like separations, it’s unclear how many children separated from their parents he considers an acceptable number.

The racial subtext comes through most clearly when Trump’s tweets on Tuesday are combined with those on Monday.

It is striking to see the president of the United States hold up a key American ally as a cautionary tale. At least he didn’t call Germany a “shithole,” though he did badly misrepresent crime in Germany, which is actually down. (On Tuesday, he claimed that crime was actually up despite statistics, and that “officials do not want to report these crimes,” an astonishing accusation to make without evidence for anyone other than Trump, who does such things regularly, including making racially inflammatory fabrications.)

What really sets Trump off, however, is the prospect of cultural change: that Germany’s white, Christian culture might be diluted by immigrants from the Middle East, Africa, and Asia—immigrants who are brown in skin color and predominantly Muslim in religion. What “we” don’t want to happen to “us,” in Trump’s words, is for nonwhite immigrants to dilute what Trump incorrectly imagines to be a stable, unchanging, and homogeneous American culture.

The immigrants at the United States’ southern border are not, for the most part, Muslim, but they are brown, and they are largely Spanish-speaking. (The linguistic supremacy of English is something that Trump values highly, even if he fails to understand the existing prevalence of Spanish in the U.S.) The Drudge Report, the conservative and usually Trump-aligned news site, made the connection between Latin American immigrants and Muslims in Europe explicit, posting a picture of children in Syria posing with a toy gun to illustrate a story about the Trump administration’s policy of separating families on the southern border.

In the case of the family separations, Trump’s tweets have once again become  a revealing window into the president’s thinking. This is not because they are more honest than what he and his aides say elsewhere—they aren’t—but because he has allowed the mask to slip, showing that what motivates his harsh border policies is not simply the imperative to enforce laws, nor a desire to deter crossings, nor even a political dispute with Democrats. It’s a matter of cultural and racial animus. For him, it always has been.

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