The Supreme Court has been asked repeatedly over four decades to answer some version of the same question: do fathers have the same right as mothers to pass on American citizenship to their children? The answer has always been “no,” with explanations rooted in the basest type of sexism that the Court decries in other contexts. But in a recent ruling, in Sessions v. Morales-Santana, the Court said “yes,” although it stopped short of providing a remedy that for the unconstitutional harm it identified.

Luis Ramón Morales-Santana was born in the Dominican Republic but has lived in the United States since he was 13. Facing deportation, he asserted U.S. citizenship at birth because his biological father was a U.S. citizen. His citizenship-by-descent claim turned initially on whether his father satisfied the requirements imposed on unwed fathers—different from and more burdensome than those imposed on unwed mothers—in order for them to pass citizenship to non-marital offspring born outside of the U.S. And his claim before the U.S. Supreme Court turned on whether Congress is constitutionally permitted to differentiate between unwed mothers and unwed fathers with respect to the numbers of years the citizen-parent had to be physically present in the United States before the child’s birth—five for fathers, but just one for mothers.

How Babies Become American Citizens at Birth: The Basic Framework

There are two basic methods for acquiring U.S. citizenship at birth: by place of birth or by descent. The Fourteenth Amendment provides for so-called birthright citizenship (jus solis)—any person born in the United States is a citizen, regardless of the citizenship of his or her parents.

But even babies born abroad can be U.S. citizens under the right circumstances. Congress has provided for citizenship-by-descent (jus sanguinis). In many countries, especially those with legal systems based on Roman law, this is the exclusive method by which individuals can acquire citizenship at birth. In the U.S., however, this method is supplemental to birthright citizenship.

Because citizenship-by-descent is not provided for in the Constitution, Congress can set the terms on which it is offered, as long as it doesn’t violate some other provision of the Constitution by doing so.

Citizenship by Descent: The Role of Legitimacy

The rules governing citizenship by descent separate children born outside of the United States into a variety of categories. The categories, and the rules that govern each one, are spelled out in the Immigration and Nationality Act of 1965 (INA), as amended in 2000 by the Child Citizenship Act (CCA).

Section 301(c) of the INA provides, for example, that a person born outside of the U.S. to two U.S. citizen parents acquires citizenship at birth as long as at least one of the parents “has had a residence in the United States or one of its outlying possessions, prior to the birth of such person.” That parent need not still be a resident, nor have been one for any particular length of time. This rule is thus relatively easy to satisfy.

What about children with one U.S. citizen parent? They are subject to different and more stringent rules, which might vary depending on both whether they were born in or out of wedlock, and whether the citizen-parent is the mother or father.

Under section 301(d), a child of married parents, one of whom is a citizen and the other of whom is an alien acquires citizenship at birth as long as the citizen-parent was, “prior to the birth of such person, physically present in the United States or its outlying possessions for a period or periods totaling not less than five years, at least two of which were after attaining the age of fourteen years.”

For children born out of wedlock, their situation differs based on the gender of the citizen-parent. A child born out of wedlock to an unwed citizen-mother acquires her U.S. citizenship as long as the mother had been physically present in the United States for at least one year at some point prior to the child’s birth. But if the citizen-parent is the child’s father, citizenship can only be transmitted to the child, under section 309(a), if certain onerous criteria are satisfied including proof of a blood relationship, an agreement in writing by the father to provide financial support throughout minority, and legal establishment of paternity before the child reaches 18. And if these criteria are met, then the in-wedlock rules apply, which additionally require that the father must have had five years of physical presence (shortened from the original rule of 10 years) in the United States prior to the child’s birth, at least two after age fourteen.

Challenges to Sex-Based Classifications in Citizenship Rules

Each of the provisions that distinguishes between mothers and fathers has been challenged. In a series of cases, until the most recent one, the Court allowed Congress to treat them differently.

In Fiallo v. Bell (1977), the Supreme Court upheld a set of rules giving alien children (those who did not acquire citizenship at birth) of citizen or lawful permanent resident mothers special immigration preferences that were not available to the children of fathers in the same categories.

In Miller v. Albright (1998), the Court took up the question whether the requirement that unwed mothers but not unwed fathers formally acknowledge their children during their minority in order to transmit citizenship to them violates the equal protection of the Fifth Amendment (the applicable provision, rather than the Fourteenth Amendment, because the law being challenged is federal rather than state). No majority opinion emerged in that case, leading the Court to accept a case raising the very same question soon thereafter.

In Nguyen v. INS (2001), the Court held that the very disparate burdens imposed on unwed fathers and unwed mothers were constitutional. Mothers are easily identified at a child’s birth because they are always there. But fathers can be hard to identify. They might not be present at the birth—and a man who is present at the birth might or might not be the father. Thus, the Court reasoned, it is reasonable for Congress to require affirmative steps to secure the legal parent-child relationship before allowing citizenship to descend to the child.

The consequences of such a rule were heartbreakingly clear in that case. The plaintiff in that case, Tuan Ahn Nguyen, was born in 1969 in Vietnam to a Vietnamese mother and an American father, Joseph Boulais. His father brought him to the U.S. as a young child after his mother abandoned him, and he raised him with his new wife in Texas. He provided financial support, care, and everything else one might expect from a parent. But he never went to court to legitimate his son, probably because he didn’t think there was any question about their parent-child relationship. But when, after conviction of a crime of moral turpitude (a trigger for deportation), Nguyen faced deportation to Vietnam, a country he knew little about and whose language he didn’t speak, the lack of legitimation meant that Nguyen could not use citizenship, transmitted through his father, as a defense. Had his mother been the citizen, he would still be here today.

The Court was convinced—though I am not—that Congress had a sufficiently important interest being served by the sex-based classification at issue in Nguyen. Since the early 1970s, equal protection doctrine has called for proof of an exceedingly persuasive justification for a law that treats men and women differently. Congress asserted two interests in Nguyen—preventing fraudulent citizenship claims and ensuring the establishment of ties between the child and the United States. These may be valid interests, but the means chosen were not closely enough related to justify the discrimination on the basis of sex. The first could be met by a requirement that paternity be established at any time, rather than only before the child turns eighteen. And the second justifies a different rule for mothers and fathers only if you assume that mothers are substantially more likely to have a relationship with their children than are fathers. That is no more than an overbroad generalization of the type that usually is rejected in equal protection cases. The mother’s presence at birth is not a guarantee of a meaningful parent-child relationship (and thus ties between the child and U.S. national ideals or culture), and the father’s potential absence at birth does not preclude such a relationship. Moreover, any difference could be accommodated by requiring either a functional father-child relationship or a legally recognized one rather than both. Fathers who do not fit the stereotype of the American GI carelessly fathering children abroad and abandoning them should, at the bare minimum, be permitted to prove they deserve the same treatment as mothers.

Sessions v. Morales-Santana and the Differing Physical Presence Requirements for Mothers and Fathers

Let’s return to the claim of Luis Morales-Santana. He was born in the Dominican Republic to a U.S. citizen-father, José Morales, and a Dominican mother. He moved to the United States at age 13 and attended public school in New York City. His father had lived in the United States from his own birth until twenty days before his nineteenth birthday in 1919 before moving to the Dominican Republic for work. Luis was not born until 1962—forty-three years later—but this twenty-day period in his father’s life, from 98 years ago, is central to his claim. Under the version of the citizenship law then in effect, Luis’ father could not transmit citizenship to a foreign-born child unless he had resided in the United States for ten years, five of which had to occur after his fourteenth birthday, before the child’s birth. José lived in the U.S. for enough years, but not the right years. Had he stayed to celebrate his nineteenth birthday in the United States, his son would have been deemed a citizen from birth—and thus not the subject of a deportation proceeding at age 55.

Luis’s claim is rooted in the differential treatment of mothers and fathers in this scheme. His parents were not married at the time of his birth, although they would eventually marry each other. Had his mother been the U.S. citizen, she would only have needed one year of physical presence in the United States prior to Luis’s birth. To say the same thing a slightly different way, had José been a woman, his son would be a citizen. That sort of sex-based classification cannot survive an equal protection challenge without meeting the standard articulated above.

This provision of the citizenship law was challenged just a few years ago in Flores-Villar v. United States (2011). There, the citizen-father was only sixteen at the time his child was born, making it physically impossible that he could have spent five of the then-required ten years in the United States after his fourteenth birthday. The U.S. Court of Appeals for the Ninth Circuit ruled against him, noting that it felt bound by Nguyen. Although the Supreme Court reviewed the case, it issued only a one-sentence opinion noting that the appellate court was affirmed by a vote of 4-4. Justice Kagan had not been confirmed in time to participate in the case. Thus, when Morales-Santana faced deportation, the constitutional question remained unresolved.

In an opinion written by Justice Ruth Bader Ginsburg, the architect of modern equal protection doctrine, the Court held that the disparate physical presence requirements for men and women constitute unconstitutional sex discrimination. It did so without revisiting the holding in Nguyen, concluding only that the physical presence requirement was not justified by any difference between citizen-mothers and citizen-fathers. No biological difference could explain disparate number of years required in the United States prior to the child’s birth. Citing the decision below, Justice Ginsburg wrote that “a man needs no more time in the United States than a woman ‘in order to have assimilated citizenship-related values to transmit to [his] child.’” Rather, the distinction flew in the face of decades of rulings designed to eliminate archaic generalizations and stereotypes from American law.

In a series of cases in the 1970s and 1980s, the Supreme Court struck down a wide range of state laws that categorically refused to recognize a parent-child relationship between an unwed father and his offspring for purposes of inheritance, custody, vetoing proposed adoptions, and so on. These rulings did not mean that states could no longer differentiate between unwed mothers and fathers, but they did mean that the government had to do so in a way that was closely related to its desired (and important) ends. The Court also struck down a wide range of sex-based classifications on grounds that they reflected archaic and overbroad generalizations.

The provision at issue in Morales-Santana, enacted in 1952, is perhaps a creature of its time—a time when unwed fathers were at best only loosely tied to their children by law. But, the provision that deprives Luis of citizenship would apply even if his mother and father had been married. Only an unwed mother can transmit citizenship based solely on a one-year period of physical presence in the United States. Married mothers and father, and unwed fathers, were all subject to the ten-year-presence requirement.

Justice Ginsburg wrote at length about the stereotypes and generalizations embodied in this scheme.

The government’s ostensible justification for the differing treatment of unwed mothers versus fathers is a concern about “stateless” children. According to the brief the United States filed with the Supreme Court, many countries grant citizenship to children based only on their parent’s nationality, rather than on the children’s place of birth. And for out-of-wedlock children, only the blood tie with the mother might be recognized. Thus, the argument goes, a child born out of wedlock and outside the United States to a U.S.-citizen-mother might have no nationality at all, unless the United States allows the transmission of citizenship through the unwed mother.

Statelessness sounds like a valid concern but, among other problems, it does not seem like Congress was actually concerned with it. Under heightened scrutiny, the government must defend its classification with an actual reason rather than just a plausible one. Citing repeatedly the work of law professor Kristin Collins, Justice Ginsburg questioned the authenticity of this explanation. In a painstaking effort, Professor Collins examined all relevant legislative documents and found little or no discussion of statelessness as a problem to be remedied by these particular rules. Rather, Justice Ginsburg concluded that the disparate rules were animated by the assumption that mothers play a different role in children’s lives than fathers. Mothers were the natural guardians of illegitimate children—indeed, for most of American history, nonmarital children were deemed fatherless by law. Citizenship law was rife with rules that reinforced the notion that children of a marriage belonged to the father, but children born out of wedlock belonged to the mother. The shorter physical presence requirement makes sense only if one assumes that children will be naturally bonded to their mothers—and thus not likely to fall prey to the competing national commitments of the alien father even if the mother’s ties to the United States are relatively weak. But if that same child is connected only to the United States through his or her father, who is assumed not to be play a meaningful role in the child’s life, then it becomes more important that the father have strong ties to the United States—demonstrated through a significant period of physical presence prior to the child’s birth. In other words, if parent is the connection between child and country, at least one side of the equation needs to be strong. But the only reason to differentiate in the requirements for ties between parent and country is if one indulges the stereotyped assumptions about the ties between children and mothers versus fathers.

For Luis Morales-Santana, A Wrong Without a Remedy

Although the Court in Morales-Santana held it unconstitutional to impose different physical presence requirements on mothers versus fathers, it did not order that Luis be granted citizenship. Equal protection doctrine demands only formal equality—that likes be treated alike. And that can be accomplished either by withdrawing the benefit from the privileged class or extending it to the excluded class. The usual remedy in equal protection cases is the latter; plaintiffs successfully prove that they have been wrongfully denied a benefit, and the remedy is to grant it to them. But the majority in this case declined to go that route. Instead, it held that the federal government cannot grant citizenship to children of citizen-mothers based only on a single year of physical presence in future cases. Thus, children of citizen-mothers and citizen-fathers will be treated equally. That is of no help to Luis Morales-Santana, who will likely face deportation on remand. (My fellow columnist, Michael Dorf, considers this choice of remedy in his column on this case, as well as whether the Court’s refusal to defer to Congress’s explanation for the difference is likely to have any bearing on the ongoing challenges against Trump’s travel ban.)

The majority opinion explains that the appropriate remedy is one that best approximates Congress’s intent underlying the statute. Here, because only unwed mothers benefited from the shorter physical presence requirement, Justice Ginsburg labeled it an “exception” to the general rule. And the majority thought it more likely that Congress, if asked, would prefer to eliminate the exception for one group than apply it across the board. Reasonable minds could disagree about whether this is the right approach, but it might have been a compromise to get five votes for the ruling on the merits.

Leveling down does cure the problem of archaic generalizations about parents based on gender, but might harm women and their children in a very tangible way. Romantic ideals about the uniqueness of motherhood perpetuate the notion that women, rather than men, should assume responsibility for children. They also contribute to negative stereotypes that diminish women as workers as workers, wage earners, and participants in public life. Finally, these ideals of motherhood establish and perpetuate, in converse, a less than ideal concept of fatherhood, in which it is “natural” for fathers to shirk responsibility. But this could all of have been accomplished while at the same time providing a remedy for Luis Morales-Santana who was a proven victim of this very system of discrimination.