“A state of war is not a blank check for the President.” The Bush Administration’s claims “would turn our system of checks and balances on its head.” “If civil rights are to be curtailed during wartime, it must be done openly and democratically, as the Constitution requires, rather than by silent erosion.” Nation readers have heard these kinds of things before–from me, the Nation‘s editors, the ACLU and other usual suspects. But before now, not from Justice Sandra Day O’Connor, author of the first two quotes. And certainly not from Justice Antonin Scalia, author of the third.

These judicial soundbites only begin to suggest the magnitude of the loss the Bush Administration sustained in a pair of historic Supreme Court decisions, issued June 28, on its asserted power to detain “enemy combatants.” In the case that received the most complete treatment of the issues, that of US citizen Yaser Hamdi, the Bush Administration was able to persuade only a single Justice–Clarence Thomas–to adopt its position. And the passion of the decisions suggests that the Justices may well have been responding not only to the detention cases before them but also to the Justice Department’s August 2002 “torture memo,” which argued–along lines that eerily echo the government’s argument in the detention cases–that the President in wartime is above the law. As the Supreme Court has now formally reminded the Administration, it’s President Bush, not King George.

The extent of the Administration’s loss is brought into relief by comparison with earlier Supreme Court decisions in wartime. The Court has historically bent over backward in deference to claims of national security, upholding the incarceration of more than 1,000 people for antiwar speech during World War I, and the detention of 120,000 Japanese and Japanese-Americans on the basis of race during World War II. The last time the Court confronted the claims of “enemy combatants,” during World War II, it refused foreign nationals incarcerated abroad any access to the courts, and upheld without opinion death penalties imposed in a secret trial on several would-be saboteurs captured here, writing its opinion only after the defendants had been executed.

This time, the Court pointedly refused to defer to the Administration during wartime. It ruled that foreign nationals held at Guantánamo have a right to file habeas corpus petitions in federal court to challenge the legality of their detentions. And in Hamdi’s case, it established that US citizens are entitled at a minimum to a fair hearing on whether they are “enemy combatants” before they can be held for a sustained period. The Court ducked the third case–that of José Padilla, a US citizen arrested at O’Hare airport–on jurisdictional grounds; his lawyers filed their challenge in the wrong court. But it is clear that when he refiles in the correct court, Padilla will be entitled to at least as much as Hamdi, and perhaps more.

The rulings do not mean that the detainees will necessarily be released anytime soon. The Court rejected, for example, the broadest challenge to the detention of US citizens. In the Hamdi case, a majority ruled that Congress’s authorization of the use of military force against Al Qaeda and those who harbor them permits the executive to hold in military custody even US citizens who are fighting for the enemy against us.

But the rulings do make it likely that all the detainees will get some sort of hearing to assess their status. In Hamdi’s case, the Court specified what process was due: notice of the charges and an opportunity to contest them before an impartial adjudicator. The Court did not reach the question of what process the Guantánamo detainees are due, because the only question before it was whether the detainees could even file a case in federal court. But there will be tremendous pressure now to give them what the Geneva Conventions require: a hearing before a military commission to determine their status.

The broader significance of the rulings lies in their ringing rejection of the argument that to defeat terrorism, the executive must have unfettered discretion. Since September 11, the Administration has repeatedly insisted that citizens (and indeed the world) should just “trust us.” George W. Bush has done more than perhaps anyone to demonstrate the poverty of that theory. We’ve been asked to trust him about weapons of mass destruction in Iraq, torture of detainees, the designation of enemy combatants, alleged relationships between Al Qaeda and Iraq, and the privacy and liberty of American citizens. With any luck, the Supreme Court’s message–that we trust checks and balances, not imperial presidents–will be heard far and wide.