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The court will probably also respond to the first words of the president’s March 19 brief, which asserts that “The ‘main object’ of the Citizenship Clause was to grant citizenship to freed slaves and their children.” That is a polite version of a more informal claim he has made elsewhere, that birthright citizenship was intended only for “the babies of slaves.”

However the court decides, history shows that Mr. Trump is wrong.

Yes, the 14th Amendment affirmed the citizenship of all Black Americans, most of whom were either newly freed or descended from people who had been enslaved. However, Mr. Trump’s extremely narrow interpretation disregards the historical record. The Senate arrived at the final language of the Citizenship Clause only after a robust debate about the implications of writing birthright citizenship into the Constitution.

The 39th Congress took up the citizenship question amid a broader effort to set the nation on a new, more inclusive course after the Civil War. At the end of 1865, it established a Joint Committee on Reconstruction, which began drafting the 14th Amendment.
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The House passed a version of the amendment that did not include the now familiar Citizenship Clause. In the Senate, however, Jacob Howard, Republican of Michigan, argued that such a clause was needed. He noted the absence of a concrete definition of citizenship — and who was entitled to it — in the existing Constitution: “It is not, perhaps, very easy to define with accuracy what is meant by the expression ‘citizen of the United States,’ although that expression occurs twice in the Constitution.”

During another round of deliberations on the wording of the amendment, Howard returned to the issue of citizenship, asserting that the amendment needed to clear the matter up. He proposed the wording that was the basis for the Citizenship Clause, which, he said, was “simply declaratory of what I regard as the law of the land already,” that “every person born within the limits of the United States and subject to their jurisdiction is by virtue of natural law and national law a citizen.”

Senator Edgar Cowan of Pennsylvania was incredulous that his colleagues intended to extend citizenship so broadly. He asked, “Is it proposed that the people of California are to remain quiescent while they are overrun by a flood of immigration of the Mongol race?”

Cowan continued with a statement that presaged the blood-and-soil populism that is part of today’s political debates, suggesting that if the children of Chinese immigrants, for example, desire the rights of a citizen, they should look to China, not the United States: “If I desire the exercise of my rights I ought to go to my own people, the people of my own blood and lineage.” Cowan prompted Senator John Conness of California to weigh in. Conness, who had himself emigrated from Ireland, affirmed the inclusive principle generally supported by Republicans of that era: “I voted for the proposition to declare that the children of all parentage whatever, born in California, should be regarded and treated as citizens of the United States.”
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Later in the debate, Senator Thomas Hendricks, a Democrat from Indiana, argued that the very nature of American citizenship would be degraded if it were extended to “the Negroes, the coolies and the Indians.” As crudely as that sentiment might strike us today, it did serve to illustrate clearly that what was up for debate was not citizenship for only Black Americans but also for people of many different ethnicities and origins.

In 1866, the amendment was approved by both houses of Congress. It was ratified by the states in 1868.