(The Lion) — The Supreme Court ruled against President Donald Trump’s birthright citizenship executive order Tuesday.

The court ruled 6-3 in Trump v. Barbara that children of illegal migrants and foreign nationals born in the U.S. are considered American citizens. Trump’s day-one executive order on the matter was aimed at protecting American citizenship.

“Children born in the United States to parents unlawfully or temporarily present are ‘subject to the jurisdiction’ of the United States and are citizens at birth under the Fourteenth Amendment’s Citizenship Clause,” Chief Justice John Roberts wrote for the majority. Justices Clarence Thomas, Samuel Alito and Neil Gorsuch dissented.

The executive order argued that “the Fourteenth Amendment has never been interpreted to extend citizenship universally to everyone born within the United States. The Fourteenth Amendment has always excluded from birthright citizenship persons who were born in the United States but not “subject to the jurisdiction thereof.”

The court held that the Fourteenth Amendment’s Citizenship Clause mirrored English common law’s criteria for citizenship, with Roberts writing that “a child born on American soil and subject to American law was made an American citizen.”

In Thomas’ dissent, he wrote that “the Citizenship Clause added greatly to the dignity and glory of American citizenship. Today’s opinion devalues that citizenship.”

“This is one of the most important decisions in the history of the Court, and in my judgment, the Court has made a serious mistake,” Alito wrote in his dissent.