In recent decisions, conservatives on the Supreme Court overturned or trimmed lower court rulings against the Trump administration.

At the same time, however, the American Civil Liberties Union and its allies also took a victory lap. Lee Gelernt, the lead counsel for the immigrant plaintiffs in the case and the deputy director of the A.C.L.U.’s Immigrants’ Rights Project said the case represented an important victory.

By defying the Justices’ ruling on a man mistakenly sent to El Salvador, the Administration has shown that it is not owed the deference typically shown to the executive branch.