For a nation of immigrants, the United States has worked hard to keep foreigners out.

The Statue of Liberty was less than 40 years old when President Calvin Coolidge signed the Immigration Act of 1924. It barred immigration from most of Asia. It cut the overall quota of immigration from countries outside the Americas in half. And it limited immigrants from other countries to 2 percent of the number of people of that country’s ancestry in the United States in 1890 — restricting immigration mostly to people from Northern and Western Europe. Those from Eastern and Southern Europe, not to say Africans, brought too many “types of social inadequacy.”

“Physically, the bodies of recent immigrants are sounder than those of the average American stock,” Harry H. Laughlin, appointed “expert eugenics agent” to the House Committee on Immigration and Naturalization, noted in 1922 testimony. “But with this sound body we have recently admitted inferior mental and social qualities of a constitutional nature which neither education nor better environment can be expected to raise above, or even to approximate, the average of the American descended from older immigrants.”

The quota system was overhauled in 1965, and immigration law today is more evenhanded. Still, the suspicion of immigrants as threats to society remains close to the surface. By claiming that people from Muslim nations threaten national security, that Mexicans are drug dealers and rapists, that immigrants take the jobs of Americans or burden taxpayers by reliance on welfare, President Trump has drawn it back to the center of political debate.

This time, suspicion is being buttressed by some economists with a proposition not too dissimilar to Laughlin’s: that immigrants could sap America’s vitality by bringing inferior cultural traits from their dysfunctional home countries to erode American social norms.