Boumediene v. Bush is one of the most important Supreme Court decisions in recent years.[1] The Court held by a 5–4 vote that aliens detained as enemy combatants in Guantánamo have a constitutional right to challenge their detention in American courts. The decision frees none of them, some of whom have been held without trial for six years, but it makes it possible for them to argue to a federal district court judge that the administration has no factual or legal ground for imprisoning them. If that judge is persuaded, he must order their release. American law has never before recognized that aliens imprisoned by the United States abroad have such rights. The disgrace of Guantánamo has produced a landmark change in our constitutional practice.

The case raised complex constitutional issues that I must describe, but the principle the Court vindicated is simple and clear. Since before Magna Carta, Anglo-American law has insisted that anyone imprisoned has the right to require his jailor to show a justification in a court of law. (The technical device through which this right is exercised is called a writ of habeas corpus. Addressed to the jailor, it announces that he has custody of a certain person's body and demands that he justify that custody.)

The Bush administration, as part of its so-called "war on terror," created a unique category of prisoners that it claims have no such right because they are aliens, not citizens, and because they are held not in an American prison but in foreign territory. The administration labels them enemy combatants but refuses to treat them as prisoners of war with the protection that status gives. It calls them outlaws but refuses them the rights of anyone else accused of a crime. It keeps them locked up behind barbed wire and interrogates them under torture. The Supreme Court has now declared that this shameful episode in our history must end. By implication, moreover, the decision goes even further. It undermines the assumption, widespread among lawyers and scholars for decades, that the Constitution as a whole offers substantially less protection against American tyranny to foreigners than it does to America's own citizens.

Boumediene was decided by the slimmest of margins. The Court now often divides, in cases of high importance, into a conservative phalanx of Chief Justice John Roberts and Justices Antonin Scalia, Clarence Thomas, and Samuel Alito, and a more liberal group of Justices John Paul Stevens, David Souter, Ruth Ginsberg, and Stephen Breyer.[2] The ninth justice, Anthony Kennedy, holds the balance of power; in this case he rejected the phalanx, joined the more liberal group, and wrote the Court's opinion on their behalf.

The conservatives were outraged but self-contradictory in dissent. Roberts declared that the Court's decision would have at best a "modest" impact and would be of no use to the detainees because it left them, as a practical matter, with no more opportunity for freedom than they had before. If anything, he said, the decision made it less likely that any of them would be released soon. Scalia insisted, with his usual splenetic flamboyance, that the decision would free dangerous terrorists and "almost certainly cause more Americans to be killed." Each of the four conservatives signed both dissenting opinions, apparently unconcerned by the contradiction.

Senator John McCain called the decision "one of the worst" in the country's history. The conservative press was horrified: The Wall Street Journal said that Kennedy had turned the Constitution into a "suicide pact." No one explained why it would destroy America to allow people who claim innocence of any crime, or threat, a chance to defend that claim before an American judge who is presumably just as worried about his family's security as the president is. Why would it be suicidal to allow them the same opportunity for defense that we allow people indicted as serial killers?

Senator Barack Obama, on the other hand, welcomed the decision, so the Court's action may well become an important issue in the coming presidential election. McCain has already promised that if elected he will appoint more justices like Roberts and Alito. It would take only one such appointment to make further decisions like Boumediene impossible, and probably reverse that decision itself.