By a bare 5 to 4 majority last week, the U.S. Supreme Court confirmed what should have been obvious:

• No president is above the law, especially when it comes to depriving people of their liberty.

• No prisoner may be denied the minimum protection of the law, regardless of his citizenship or how dangerous the government claims he is.

People imprisoned by the United States have a right to challenge the legal basis for their detention before a neutral magistrate. They must get due process: a real chance to know the evidence against them and confront their accusers. The government must justify a person’s detention or set him free.

This is the purpose of the writ of habeas corpus — the “Great Writ,” as it is called.

These rights are what the U.S. Supreme Court upheld last week in Boumediene v. Bush, a case involving prisoners held at the U.S. Naval Station at Guantanamo Bay, Cuba, many for more than six years.

No legal principle is more important to a free people. None should be more deeply cherished. And it is this principle that the Supreme Court majority reaffirmed last week.

Does this mean that the people declared to be “unlawful enemy combatants” by President George W. Bush suddenly will be released? No. It means that they must get a fair chance to challenge in federal civilian courts the legal basis for their detention.

The Constitution provides that the Great Writ may “be suspended . . . when in Cases of Rebellion or Invasion the public Safety may require it.” But the Court ruled that that was not the case in Boumediene.

Consider what the Bush administration — sometimes with the assistance of a Republican majority in Congress — has tried to do to deny the constitutional right of the Great Writ:

• Mr. Bush claimed — initially without action by Congress — that as commander in chief, he had the right to imprison anyone he classified as an enemy combatant, even U.S. citizens, and hold them indefinitely without filing charges against them, without allowing them to seek legal counsel and without any right to challenge their detention.

• The Bush administration also argued that prisoners at the Guantanamo Bay military installation were outside the United States and, therefore, not entitled to any constitutional protections.

• After earlier Supreme Court decisions knocked down these arguments, Congress became involved and pushed through legislation stripping the federal courts of the authority to rule on habeas corpus claims by Guantanamo prisoners. Last week’s ruling invalidated that move.

• Left standing were other legislative provisions establishing military commissions to try suspects at Guantanamo, proceedings that a growing number of military and civilian lawyers and judges have begun criticizing as the equivalent of kangaroo courts.

Chief Justice John Roberts Jr. filed a lengthy dissent to the majority decision in Boumediene that is petulant in tone and full of lawyerly quibbles. It contends that as a result of this decision, everyone loses — including the American people.

In fact, everyone wins — at least, everyone who believes in a constitutional system that limits the power of government to imprison people and empowers the judiciary to enforce those limits.