IMAGINE ONE of those wrenching custody cases in which every side seems to have the child’s interests at heart but almost every fact is disputed. Many people — including the child in the middle of the fight — have pain ahead of them, no matter the outcome. Now mix in America’s historical mistreatment of Native Americans and a major disagreement over a decades-old law meant to redress some of those wrongs, and you get the emotionally fraught tangle that the Supreme Court will consider Tuesday.

When Christinna Maldonado gave birth to Veronica, she had already selected Matt and Melanie Capobianco to be her daughter’s adoptive parents. The father, Dusten Brown, hadn’t supported Ms. Maldonado during her pregnancy, and he renounced his parental rights to her in a text message. But after he heard that Veronica would grow up with the Capobiancos, not her biological mother, Mr. Brown moved to obtain custody of the child. He wouldn’t have had much of a case except that he is part Native American, and a federal law, the Indian Child Welfare Act, puts restrictions on the adoption of Native American children. After they had cared for Baby Veronica for two years, a South Carolina court made the Capobiancos give her back in 2011.

Mr. Brown is a registered member of the Cherokee Nation, his daughter is 3/256th Cherokee, and he now wants custody of his biological daughter. Even though Veronica’s mother is not Native American, never married Mr. Brown and had custody of the child when she put her up for adoption, he points out that the law forbids placing a child with a non-Indian family unless keeping the child with her biological parents would hurt her. Even then, there is supposed to be a preference for placing the child in another Native American home.

The Capobiancos point out that Mr. Brown wasn’t a parent in any substantive sense at the time of adoption. He refused to pay child support to Veronica’s mother. He even signed a formal notice of adoption, though he claims he did not realize its implications. It’s true that Congress wrote some very strong protections into the law. They were intending to prevent the forcible breakup of Native American families, a shameful past practice. Yet lawmakers surely did not mean to protect the rights of Native American biological parents to the point that a child’s unwed, absent father can undo an adoption that her biological mother and legal custodian determined to be in her best interests, merely because she has a drop of Native American blood in her.

If the justices rule against the Capobiancos, Congress should step in and fashion some sensible limits to the Indian Child Welfare Act.