Does the president have the power to order the military to seize an American citizen on American soil, declare him an outlaw to the Constitution, and lock him up for the duration of the war on terror — in other words, forever? That’s the stark question the Supreme Court will be examining today, April 28, when it hears oral argument in Padilla v. Rumsfeld.

Padilla, an American born in Chicago, was arrested by federal agents at O’Hare International Airport in May 2002, and held on a material witness warrant. Two days before a hearing in federal court on the validity of that warrant, the president declared Padilla an “enemy combatant” plotting a “dirty bomb” attack in the United States, and ordered him transferred to a naval brig in South Carolina, 700 miles away from his lawyer. Padilla has been held there for nearly two years without charges or meaningful access to counsel.

There’s little in Padilla’s background to suggest he’s an innocent man wrongly accused — he’s a violent ex-con with apparent ties to Al Qaeda. But “the innocent have nothing to fear” is cold comfort and poor constitutional argument. The very principle that imprisons the guilty can be used to seize the innocent.

And the principle the government is advancing is broad indeed. It amounts to the assertion that the executive branch can serve as judge, jury, and jailer in cases involving terrorist suspects. Of all the powers claimed by the president since September 11, that power is the one most to be feared — not least because, due to the nature of the war on terrorism, it’s a power unlikely ever to be relinquished.

Moreover, it’s a power that cannot be found in the Constitution. The Bill of Rights does not come with an asterisk reading “unenforceable during time of war.” As the Supreme Court declared in Ex Parte Milligan (1866), rejecting the military trial of a civilian during the Civil War, “The Constitution of the United States is a law for rulers and people, equally in war and in peace, and covers with the shield of its protection all classes of men, at all times.”

Congress can suspend the writ of habeas corpus under very narrow circumstances “when in Cases of Rebellion or Invasion the public Safety may require it.” But Congress has made no such attempt here — instead the president has unilaterally stripped Padilla of his rights, holding him without even a semblance of due process.

The government justifies its confinement of Padilla by citing a five-and-a-half-page “Declaration” by Michael Mobbs, an obscure Pentagon bureaucrat who has never been cross-examined by Padilla’s attorneys. A look at the Mobbs Declaration reveals just how far down the rabbit hole we’ve traveled. Of the confidential informants who fingered Padilla, the declaration notes: “Some information provided by the sources remains uncorroborated and may be part of an effort to mislead or confuse U.S. officials.… In addition, at the time of being interviewed by U.S. officials, one of the sources was being treated with various types of drugs to treat medical conditions.” Again, that’s not to suggest that Padilla is innocent. It’s to highlight the starkly extra-constitutional nature of these proceedings — in which Padilla is not permitted to test the government’s evidence in open court.

The government’s brief relies heavily on the president’s constitutional powers as “Commander-in-Chief” of the U.S. military. But as Justice Jackson put it in a 1952 case delineating the president’s wartime authority, “the Constitution did not contemplate that the title Commander-in-Chief of the Army and Navy will constitute him also Commander-in-Chief of the country, its industries and its inhabitants.” The Bush administration has repudiated that theory of limited executive power in favor of one that is essentially limitless.

Thus far, President Bush has wielded this vast power sparingly. But he will not be the last president to wield it. The proponents of this sweeping claim of executive power have no answer to that, save to urge us to elect good men. Our entire constitutional structure is based on a repudiation of that fond notion.

Arguing before the Supreme Court in the Milligan case, James Garfield, who would later serve as 20th president of the United States, declared that a decision to uphold the constitutional limits on executive power would show the world “that a republic can wield the vast enginery of war without breaking down the safeguards of liberty.” A decision that denies Padilla his day in court will have the opposite effect. It will declare that the articles in the Bill of Rights are mere peace provisions in an era of permanent war. That’s a terrifying concept indeed.