Birthright citizenship is the principle that every baby born in the United States is a U.S. citizen. The Constitution's 14th Amendment guarantees the citizenship of all children born in the United States (with the extremely narrow exception of children of foreign diplomats) regardless of race, color, or ancestry.

But on June 27, 2025, the Supreme Court significantly limited this judicial power. In Trump v. CASA Inc., a 6-3 majority ruled that federal courts likely lack the authority to issue “universal injunctions” that block government policies nationwide.

The Supreme Court stated that the rule was "ancient and fundamental", i.e., well-established common law, in 1898: "the Fourteenth Amendment affirms the ancient and fundamental rule of citizenship by birth within the territory, in the allegiance and under the protection of the country, including all children here born ...