Tomorrow the Supreme Court will consider whether American fathers have the same rights as American mothers to ensure that their children are citizens at birth. Under the 14th Amendment, “all persons born in the United States are … citizens of the United States.” But the status of children born to American parents beyond U.S. borders is less certain. In the case Flores-Villar v. United States, the Justice Department is defending the constitutionality of a law that treats some of these children differently depending on whether their mother or their father is a citizen. The government relies on a speculative reading of the historical record and dismisses clear evidence that such laws perpetuate centuries-old stereotypes regarding men’s and women’s roles as parents. The court should strike down the statute and its sorely out-of-date approach.

For well over a century, an American woman who married a noncitizen could do nothing to ensure citizenship for her foreign-born child. The presumption was that in marriage, fathers had full authority and determined their children’s political and cultural identities. When a child was born outside marriage, by contrast, the view was that the mother “stands in place of the father”—she bore responsibility; he escaped unburdened. In such circumstances, the mother could be the source of her foreign-born child’s citizenship.

In the 1920s and 1930s, women’s organizations worked tirelessly in Congress to tear down this old structure. Within marriage, they succeeded. As a result, when a child is born on foreign soil to one American citizen and one non-citizen, and the couple is married, our citizenship laws treat the child the same regardless of whether the American parent is the mother or the father.

But for children born outside of marriage on foreign soil, the old presumptions linger. It remains the case under our citizenship laws that these children are treated differently depending on whether their mother or father is the American citizen. If an American mother isn’t married, she need only satisfy a single requirement to ensure that her foreign-born child is an American citizen: She must have lived in the United States for one year at any point during her life. By contrast, an unmarried American father faces an extensive, and sometimes impossible, set of hurdles, as the father of Ruben Flores-Villar Jr. learned.

Ruben Jr., named for his father, was born in Mexico in 1974. When he was 2 months old, his father and grandmother—both American citizens—brought him to the United States for much-needed medical care. From that point, Ruben Jr.’s mother played virtually no role in his life. Ruben Jr. was raised in America from infancy, in his father’s household. If the roles had been reversed, and his American parent had been his mother, his path to citizenship would have been simple and attainable. But the law holds that Ruben Sr. cannot confer citizenship unless he provides proof of parenthood, legally acknowledges Ruben Jr. before the child turns 18, and pledges to support him. Finally—and crucially in this case—Ruben Sr. must show that he himself lived in America for at least five years, after he turned 14 and before Ruben Jr.’s birth. Ruben Sr. satisfied all the legal requirements save the last one, which was physically impossible: He was only 16 when Ruben Jr. was born.

What is the logic behind making it harder for American fathers than it is for American mothers to secure citizenship for their children born abroad outside marriage? Our system is rooted in old English law, adopted in the new United States, under which the unmarried mother was “bound” to support and raise “the bastard child,” while the father’s obligations were few and often unenforced. This asymmetrical understanding of parental responsibility had harsh and sometimes racist implications when applied in the citizenship context. As one legal scholar explained in 1915, “It seems clear that the illegitimate half-castes born in semi-barbarous countries of American fathers to native women are not American citizens.”

In 1998 and again in 2001, the Supreme Court sustained a related set of gender-based requirements in our citizenship laws (involving legal acknowledgement of the child), partially out of concern that children “fathered by U.S. servicemen when serving a tour of duty overseas” would claim citizenship. The fear that “war babies” would come knocking on their fathers’ doors colored the court’s reasoning in those cases, even though the fathers in the particular suits at issue had substantial relationships with their children. The court’s logic is troubling from the perspective of sex equality. As then-Justice Sandra Day O’Connor explained in a dissenting opinion, our sex-based citizenship laws are “paradigmatic of a historic regime that left women with responsibility, and freed men from responsibility, for nonmarital children.”

As Ruben Sr. learned, however, a system that assumes all unmarried fathers are irresponsible sometimes punishes the father who embraces and raises his child.

In defending the differential treatment of fathers and mothers in our citizenship laws as constitutional, the government in Flores-Villar has urged that there is a benevolent basis for the discrimination. Invoking the specter of the classic story, “The Man Without a Country,” DoJ argues that these laws treat American mothers differently in order to protect their children from statelessness. The foreign-born child of an unmarried American father “is unlikely to be born stateless,” the government argues, because “the child will have the citizenship of the mother.”

The government’s support for this assertion is questionable at best. It is also based on a fanciful reading of the legislative record. We have reviewed thousands of pages of congressional debates and legislative hearings stretching from the 1920s through the present. We find no evidence that Congress has ever been seriously concerned about a special risk of statelessness facing the foreign-born out-of-wedlock children of American mothers. Instead, the record includes mountains of evidence that Congress has routinely relied on sex-based stereotypes when crafting citizenship laws. When Congress makes sex-based distinctions because of outdated presumptions about the proper roles of men and women as parents, it collides with the guarantee of equality in the Constitution.

The government dismisses these arguments about sex-discrimination in part by highlighting the facts that brought Ruben Jr. to court: He was convicted of importing marijuana and has been deported. Unless he is found to be a citizen, he will never be allowed to return to the United States. The government argues that if Ruben Jr. had stayed on the right side of the law, he would be eligible to become a citizen through naturalization.

This is a distraction. Flores-Villar isn’t a case about keeping out illegal immigrants. It is a case about the rights of American mothers and fathers to equal protection of the law. It is also about a child’s “right to a nationality,” a fundamental principle of the Universal Declaration of Human Rights. “Citizenship is not a license that expires on misbehavior,” the Supreme Court forthrightly stated more than 50 years ago. Nor should one’s citizenship status turn on the happenstance of whether one’s citizen parent is a mother or a father. Either parent can take responsibility for raising a child. That’s the modern truth the Supreme Court should embrace and that our citizenship laws should reflect.

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