“This is one of the most important decisions in the history of the Court,” Justice Samuel Alito wrote in his dissent in Trump v. Barbara, on the meaning of birthright citizenship, “and in my judgment, the Court has made a serious mistake.” It’s a very good thing that Alito is so disappointed, because he’s right about the case’s importance. For the moment, Donald Trump’s attempt to rewrite the Constitution—which, as the Court recognized on Tuesday, in its final ruling of the year, grants birthright citizenship to almost anyone born in the United States—has failed. Trump had tried to decree, by executive order, that the children of mothers who had no legal status in the U.S., or whose status was legal but temporary, and whose fathers were neither citizens nor permanent legal residents at the time of their birth, would not be citizens. (The order had not yet gone into effect, due to the legal proceedings.) And Trump lost.

Barbara—which takes its name from the pseudonym of a mother whose baby might have been affected by Trump’s executive order—is a case worth celebrating. The majority opinion, written by Chief Justice John Roberts, contains soaring language about the commitment that the Fourteenth Amendment makes to babies born in this country. “We keep that promise today,” the opinion says. But only five Justices out of nine signed on as promise-keepers: Roberts, Amy Coney Barrett, Elena Kagan, Ketanji Brown Jackson, and Sonia Sotomayor. Alito was not alone, and neither, on this issue, is Trump.

Alito, Clarence Thomas, and Neil Gorsuch each wrote separate dissents in Barbara, and Gorsuch joined Thomas’s. Brett Kavanaugh wrote a partial concurrence that was also a dissent: he didn’t think that the Fourteenth Amendment’s Citizenship Clause necessarily promised anything to children of “foreign citizens unlawfully or temporarily in the country.” But he accepted that Congress thought the amendment did so when it incorporated its language into the Nationality Act of 1940, and into subsequent updates to immigration laws. And so Kavanaugh believes that Trump’s executive order is unlawful—but not unconstitutional. As a result, the decision was 6–3 on the illegality of the executive order, but only 5–4 on the constitutional question.

The distinction is important because, according to Kavanaugh’s logic, what Congress gives, it can also take away: it could pass a law stripping citizenship from many American-born babies, even if Trump, acting alone, cannot. Trump responded to the ruling by pretending that Kavanaugh’s view was already the law, writing on Truth Social, “Congress should start TODAY to work on ending expensive and unfair to our Country, Birthright Citizenship. They will have my Complete and Total Support!” He is wrong, but his post is an indication of what was at stake, and of the continuing risk. Had Kavanaugh convinced just one other conservative Justice (either Roberts or Barrett) that narrowly overturning the executive order on those statutory grounds was the best way to resolve the case, the meaning of American citizenship would have been very different today than it was yesterday. The case was much too close.

The question, after all, had seemed settled. The Fourteenth Amendment, ratified in 1868, holds that “persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.” As the Supreme Court affirmed in U.S. v. Wong Kim Ark—a case, decided in 1898, involving a man born in San Francisco to noncitizen immigrants from China—the only exceptions, derived from the phrase “subject to the jurisdiction thereof” involve children of diplomats, of members of occupying armies, or of certain Native American tribes, or those who were born on foreign naval ships. (The status of Native Americans changed with the Indian Citizenship Act of 1924; this case is rife with reminders that achieving justice has been a journey in this country.) The shared understanding of that reading of the Amendment has been so firm that, as one particularly powerful amicus brief in the case observed, even babies who were born in Second World War internment camps to Japanese American parents who had renounced their own U.S. citizenship and were on the verge of being deported were nonetheless recognized as birthright citizens.

For Roberts, those exceptions are grounded in “intersovereign concerns” not relevant to the babies who would have been denied citizenship under Trump’s executive order. As the majority opinion in Barbara notes, “Words appearing frequently in the Executive Order—‘mother,’ ‘father,’ ‘lawful,’ ’temporary’—are absent from the Clause. For a simple reason: they did not matter.” The Citizenship Clause is about American babies, and five Justices (or six, if you count Kavanaugh) stood by them.

At one point in the case’s oral arguments, in April, D. John Sauer, the Trump Administration’s Solicitor General, railed about how we are in “a new world now,” where “eight billion people are one plane ride away from having a child who’s a U.S. citizen.” Roberts interrupted him: “Well, it’s a new world. It’s the same Constitution.” In his opinion, Roberts’s language about the quality of the arguments on the other side is cutting, referring to a “smorgasbord of formulations” related to the idea of allegiance and to the dissent’s reliance on “a handful of ambiguous floor statements” in the Senate debates over the Fourteenth Amendment. Trump wanted a new Constitution, or at least what Roberts called a “dramatically revisionist view” of the old one. At the same time, Roberts was with the majority that handed Trump wins in two immigration cases last week, allowing him to end Temporary Protected Status for Haitians and Syrians and making it easier to turn back migrants short of the border, even those seeking asylum.

There is also, again, the disquieting realization that four Justices were willing to change the meaning of birthright citizenship, albeit to different degrees, and for varying reasons. In the case of Alito and Thomas, there is also a striking note of bitterness. Alito is focussed on the ways today’s world is unpleasantly new for him. He worries about “birth tourists” and suggests that things turned upside down because “a coterie of actors—Executive Branch officials, States and cities, and a variety of private groups—sent the message to would-be immigrants that our immigration laws should not be taken too seriously.” He adds that the consequences of ending birthright citizenship as it now exists need not be “inhumane.” At the same time, he says, there should be no fear of “rocking the boat.”

Thomas devotes much of his ninety-one-page dissent to arguing that the Citizenship Clause was meant to correct the injustice of an earlier decision, Dred Scott, which denied citizenship to Black people who “were Americans” in a way that, in Thomas’s view, the “children of foreign temporary visitors” were not. The Amendment’s Citizenship Clause, he says, was “enacted for people who were born in this country and called it home,” but has been “repurposed for political projects,” hijacked by a Court seeking “to protect its own set of preferred rights.” He doesn’t say exactly what is being taken away from whom, or why the clause can’t encompass more than one group. Ketanji Brown Jackson wrote an opinion directly responding to Thomas, who she said “elides the entire point” of the post-Civil War amendments. Jackson says they represented “an anticaste, antisubordination reset for the Nation, not a mere spot treatment for the dark stain of slavery.” Both Justices quote Frederick Douglass, but he seems far more at home with Jackson.

Gorsuch, meanwhile, thinks that the children of people with legal but temporary status, which would include those in the country on student and work visas, are not necessarily birthright citizens. But, he adds, “I harbor doubts” about whether birthright citizenship could be denied to the children of long-term residents with no legal status at all. While this position may be surprising (can a baby whose parents are here illegally be in a better position than those here legally?), it is a delicate way of noting one of the major contradictions in the Trump Administration’s case. Sauer had relied heavily on the idea that the parents of a baby had to have a “domicile” in the United States, as Wong Kim Ark’s parents did. But that notion turned out to be a slippery one; Sauer argued that people without legal status did not have the “capacity” to establish domicile even if they’d been here for decades, and had no other home. Maybe so, Gorsuch says, but “I wonder . . . If those parents are not domiciled here, then where are they domiciled?”

As Roberts notes in his opinion, from the beginning, “some wished to change the rule” on which birthright citizenship was based. The push to do away with birthright citizenship predates Trump, although he became its champion in his first campaign for President. Trump v. Barbara is a landmark, in other words, but it marks a new stage in a long fight over who gets to be American, rather than a true resolution of the question. If there was, as Alito contends, a mistake, it was in underestimating the threat that he and his ideological allies posed to our shared concept of citizenship, and to the children whose birthright it is. ♦