The thing to remember about oral arguments set for Thursday at the Supreme Court over President Trump’s vow to end birthright citizenship is that what looks like a legal slam dunk could come to resemble a jump ball. Mr. Trump is also challenging the practice of universal nationwide injunctions, which have come to bedevil the 47th president’s immigration agenda. Mr. Trump’s record before the Nine suggests America could overperform.

One of the 47th president’s earliest acts in office was an executive order mandating that children born in America would not be automatically entitled to citizenship if their parents were in this country illegally or temporarily. The 14th Amendment ordains in part that “all persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.” In key cases, judges have required birthright citizenship.

The solicitor general, John Sauer, will address the justices as he seeks to end a government losing streak, with defeats in three separate cases that the court consolidated. That the justices are hearing this emergency appeal at all, though, suggests judicial interest — even after one judge called the administration’s position “blatantly unconstitutional.” Another court reckoned, “No court in the country has ever endorsed the president’s interpretation.”

The towering Supreme Court precedent is United States v. Wong Kim Ark. That case from 1898 turned on whether a child who was born in America to Chinese parents who were lawful permanent residents was an American citizen. A 6-to-2 court held that because the child’s parents were ​not ​“employed in any diplomatic or official capacity under the Emperor of China,” they were subject to America’s “jurisdiction” — and that their child was a citizen. 

Our A.R. Hoffman has reported on an emerging argument for ending birthright citizenship. It is that illegal aliens and even temporary residents are not enmeshed in the social contract. Therefore their children are not within the ambit of citizenship. Yet it appears likely that Mr. Sauer will focus not on highfalutin social theory but instead on the lawfulness of the universal injunctions that have arrested Mr. Trump’s efforts to end birthright citizenship.

Given that birthright citizenship is now the law of the land, revoking it would require the justices to weigh how such a change of policy could be implemented — prospectively, presumably. Even if the high court determines that the parchment does not guarantee birthright citizenship, the question would loom of whether such a U-turn could be achieved by executive — or judicial — fiat or whether it would require an act of Congress.

Mr. Trump’s position is that judges ought to be able to issue only orders that cover the litigants before them and that bind only in their own jurisdictions. The government has argued that the nationwide species of injunctions “have reached epidemic proportions.” There could be a quorum on the court to curtail that power — though universal injunctions under the Administrative Procedures Act are not presented here in this appeal. 

Justice Clarence Thomas wrote, in Trump v. Hawaii, that he is “skeptical that district courts have the authority to enter universal injunctions.” Justice Neil Gorsuch, in a later case, contended that district courts may only “redress the injuries sustained by a particular plaintiff in a particular lawsuit.” Attorney General Sessions called nationwide injunctions “a threat to our constitutional order.”

While Mr. Sauer will have to win more than Justices Thomas and Gorsuch to the government’s position, his boss’s record before the high court could offer grounds for optimism. His first term travel ban was upheld in Hawaii. Mr. Trump avoided disqualification from the presidential ballot by a unanimous decision, and he secured the presumption of presidential immunity in the face of Special Counsel Jack Smith’s efforts to convict him.

The decision by Mr. Trump’s legal eagles to bundle the constitutionality of nationwide injunctions together with the birthright citizenship question could pay off even if the justices decline to ratify his narrow reading of the benefits conferred by the 14th Amendment. Just like presidential immunity, a ruling in Mr. Trump’s favor limiting injunctions to the parties of a case could apply to presidents of both parties. Talk about a slam dunk.