When Donald Trump claimed in 2015 that Mexican immigrants will ravage our women, destroy our neighborhoods, and taint our ethnic and cultural purity, he entered into a long-standing, well-cultivated American tradition of xenophobia and fear-mongering.

In the late 19th century, poet Emma Lazarus celebrated the "huddled masses yearning to breathe free" and "the wretched refuse" who came to America for a better life. But Prescott F. Hall, the co-founder of the powerful Immigration Restriction League, offered a rebuttal verse:

Enough! Enough! We want no more Of ye immigrant from a foreign shore Already is our land o'er run With toiler, beggar, thief and scum.

After over a century of mostly open borders, in which tens of millions of European immigrants became Americans, members of the WASP establishment decided in the 1920s that the United States could no longer accept what they denounced as "beaten men from beaten races." In terms that will sound familiar today, they claimed Jews, Italians, and others were incapable of assimilating into a country based on private property, limited government, and hard work.

In 1924, the restrictionists won a massive and long-lasting legislative battle with passage of The Johnson-Reed Act, which completely prohibited immigration from Asia and sharply limited immigration from Europe based on the country of origin. Under the new law, for instance, just 4,000 Italians were allowed to enter the country each year, down from an average well over 200,000 in each year of the preceding decade. National origins would remain the basis of U.S. immigration law until 1965.

The Guarded Gate: Bigotry, Eugenics, and the Law That Kept Two Generations of Jews, Italians, and Other European Immigrants Out of America, a new book by Daniel Okrent, looks at the ways in which xenophobia and pseudo-science combined to fundamentally alter immigration policy at the start of what became known as "the American Century." Okrent was the first public editor of The New York Times and is the author of Last Call, a history of Prohibition. He sat down with Reason to talk about how old debates over immigration and America's national character are newly relevant to contemporary politics.

Edited by Ian Keyser. Intro by Todd Krainin. Cameras by Jim Epstein and Kevin Alexander.

'Modum' by Kai Engel is licensed under CC By 4.0

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