The birthright citizenship provision, explained Senator Jacob Howard of Michigan, one of the founders of the Republican Party and the floor manager of the amendment’s passage in the Senate, was intended to “settle the great question of citizenship once and for all.” The amendment formed part of a constitutional revolution that, in the words of George William Curtis, the editor of the Republican magazine Harper’s Weekly, transformed a document “for white men” into one “for mankind.” In 1870, Congress amended the naturalization laws to allow black immigrants to become citizens. The bar to Asians, however, persisted; they could not be naturalized until well into the 20th century.

Mr. Trump’s prospective order would deny citizenship to children born in the United States to noncitizens. It is especially aimed at undocumented immigrants who supposedly pour into the country to have “anchor babies” — one of the president’s numerous exaggerations when it comes to the dangers posed by immigration. When the Fourteenth Amendment was ratified, the category of illegal or undocumented immigrants did not exist. The closest analogy to children born today to such immigrants were the American-born offspring of newcomers from China. At the time, their parents could not become citizens, but in 1898, following the plain language of the Fourteenth Amendment, the Supreme Court affirmed that a person of Chinese origin born in the United States was a citizen by birthright.

In the interview in which he discussed his plan to issue the executive order, Mr. Trump claimed that the United States is “the only country in the world where a person comes in and has a baby, and the baby is essentially a citizen of the United States.” This, too, is an exaggeration, as many in the Western Hemisphere do recognize birthright citizenship. But it is true that in the past decade or two the nations of Europe have retreated from this principle. All limit automatic access to citizenship in some way, making it depend not simply on place of birth but also on ethnicity, culture, religion or extra requirements for the children of parents who are not citizens.

That has not been our way. Adopted as part of the effort to purge the United States of the legacy of slavery, the principle of birthright citizenship remains an eloquent statement about the nature of American society, a powerful force for assimilation of the children of immigrants and a repudiation of our long history of racism.

Mr. Trump’s order, if issued, will not only violate both the Constitution and deeply rooted American ideals, but also set a dangerous precedent. If the president can unilaterally abrogate a provision of the Constitution by executive order, which one will be next?

Eric Foner is the author of many works of American history, including “Reconstruction: America’s Unfinished Revolution, 1866-1877.” His latest book, “The Second Founding: How the Civil War and Reconstruction Forged a Constitutional Revolution,” will appear next year.

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