Immigrants are no longer welcome in Donald Trump’s America. Instead, the Republican presidential nominee posited that under his potential second administration, he would round up and mass-deport noncitizens based on their “serial numbers.”

Speaking with Full Measure’s Sharyl Attkisson, Trump argued that the United States—which was founded by and has historically been a nation of immigrants—shouldn’t be a “dumping ground” for newcomers.

“But we’re getting the criminals out, and we’re going to do that fast, and we know who they are, and the local police know their names, and they know their serial numbers,” Trump said. “They know everything about them.”

Trump has regularly mimicked Adolf Hitler during his campaign. But the mention of serial numbers—a terrifying echo of the identification numbers forcibly tattooed on concentration camp prisoners—is one of his most chilling references yet.