Jail, or Jail Not. There Is No Try.

Chief Justice Roberts will help decide whether an indefinite war requires indefinite detention.

The senators grilling Supreme Court nominee John G. Roberts asked him so many questions about abortion, a subject on which the Constitution is silent, that they had no time to ask him about the right to due process. That's a shame, because due process is under assault by a president who claims the authority to lock up anyone he deems an "enemy combatant" until the end of the war on terrorism, which seems likely to outlast Roberts' tenure as chief justice.

Although Roberts has not directly addressed this issue, a decision announced in July by the U.S. Court of Appeals for the D.C. Circuit may provide a clue to his position. The ruling, which Roberts joined, allowed the Pentagon to proceed with its trial of Salim Ahmed Hamdan, Osama bin Laden's former driver and bodyguard, before a military commission at Guantanamo Bay.

Under the 1949 Geneva Convention, prisoners of war in an "armed conflict not of an international character occurring in the territory of one of the High Contracting Parties" (such as the fighting in Afghanistan, where Hamdan was captured) are entitled to a trial before "a regularly constituted court affording all the judicial guarantees which are recognized as indispensable by a civilized people." It is doubtful that the Pentagon's jury-rigged military commissions, which lack direct judicial review and other important safeguards, satisfy this standard.

But the D.C. Circuit ruled that Hamdan is not covered by the Geneva Convention, which in any event does not create judicially enforceable rights. Hamdan's status is debatable, and U.S. law governing military commissions arguably should be read in light of U.S.-ratified international treaties (which are, according to the Constitution, "the supreme Law of the Land"). Still, Roberts' decision to side with the government on these questions is less troubling than his apparent willingness to read the authorization of military force that Congress approved after the September 11 attacks as a license for the executive branch to treat suspected terrorists however it chooses.

Although the Bush administration so far has not sought to try American citizens accused of terrorism before military commissions, it has held them indefinitely in military custody. The U.S. Court of Appeals for the 4th Circuit recently upheld such a detention in the case of suspected terrorist Jose Padilla.

Padilla has been imprisoned without charge since he was arrested in Chicago more than three years ago. Citing Hamdi v. Rumsfeld, a 2004 Supreme Court decision involving another American accused of ties to Al Qaeda, the court concluded that Congress had implicitly approved Padilla's detention when it authorized the president to "use all necessary and appropriate force" against the perpetrators of 9/11.

In Hamdi, Justice Antonin Scalia—whom the president identified as one of the models he had in mind when he picked Roberts for the Court—took a different view. Unless Congress chooses to prevent judicial review by suspending the writ of habeas corpus, Scalia said, the government has two options when it arrests Americans suspected of links to terrorism: try them or release them.

The plurality in Hamdi did not go that far, but it did say Americans classified as enemy combatants have a right to contest that designation before "a neutral decisionmaker." What that means in practice will be determined as Padilla's case makes its way through the courts.

The important question is not whether Padilla is guilty but whether and how the government has to prove his guilt. If the president is permitted to exercise the sort of unilateral, unreviewable detention power he wants, there will be no protection against mistakes (or worse) by his administration or future administrations.

As chief justice, Roberts will play an important role in deciding exactly how much process is due in cases like this. I draw some hope from a little-noticed 2003 decision in which he found that the National Transportation Safety Board had violated the Administrative Procedure Act, which forbids "arbitrary" or "capricious" actions, when it upheld the suspension of a pilot's license.

There was no question that the pilot was guilty of the infraction that triggered the suspension. But Roberts found that the safety board had unjustifiably ignored a longstanding rule against pursuing stale complaints, flouting three of its own precedents to do so.

When Roberts hears terrorism cases, I hope he shows the same respect for process and the same aversion to letting the government make up the rules as it goes along.