What does that mean for the American people? It means the same thing it did for Jose Padilla. You’ll recall that Padilla was arrested in Chicago for terrorism and transferred to military custody, where, according to Padilla, he was tortured and involuntarily injected with drugs.

The government’s position is that since the entire world is a battlefield in which the war on terrorism is being waged, U.S. officials now have the power to arrest any American suspected of terrorism, place him in military custody, and subject him to the same “unlawful enemy combatant” treatment that Padilla received, until the war on terrorism has finally been won, no matter how long that takes.

You’ll recall that the government’s position was that Padilla, as an “unlawful enemy combatant” suspected of having committed terrorist acts, was not entitled to the procedural rights guaranteed to criminal defendants in the Bill of Rights, including the rights to counsel, due process, and trial by jury.

The district court ruled in favor of Padilla at his habeas corpus hearing, but the Second Circuit Court of Appeals reversed that decision, upholding the government’s “unlawful enemy combatant” argument for Padilla and, by implication, all other Americans.

Before the Supreme Court could rule on Padilla’s appeal from the Second Circuit’s decision, the government announced that it wished to transfer him from military control to federal-court control on the basis of a grand jury indictment charging him with terrorism. The Supreme Court permitted the transfer and declined to hear Padilla’s appeal because the case was now “moot,” given that Padilla was no longer being held by the military but instead was being held by the Justice Department as a criminal defendant. That left the Second Circuit decision upholding the “unlawful enemy combatant” designation intact.

Even if Padilla is acquitted in the federal-court action, there is little doubt that the Pentagon will immediately take him back into military custody as an “unlawful enemy combatant” in the war on terrorism, requiring Padilla to once again embark, in a habeas corpus proceeding, on a long legal journey to the Supreme Court.

Currently, under the Second Circuit’s decision in Padilla, and now also under the Military Commissions Act, the president has the power to order the military arrest and incarcerate any number of Americans suspected of terrorism. Americans would still have the right to file a petition for writ of habeas corpus in federal court because the Military Commissions Act cancelled that right only for foreigners, not Americans. Keep in mind, however, that a habeas corpus hearing is not a full-blown trial to determine guilt or innocence but is simply designed to determine whether the government has legal justification for holding a prisoner. All the government would have to do at the habeas corpus hearings is provide some evidence that the Americans it is holding in military custody have engaged in some act of terrorism and then cite the Second Circuit opinion and the Military Commissions Act in support of its power to continue detaining them.

Of course, the cases would ultimately go to the Supreme Court, but that would inevitably entail a lengthy delay, a period of time during which lots of Americans could be tortured, abused, and even “accidentally” killed, just as foreign “unlawful enemy combatants” in U.S. military custody have been. Moreover, there is no guarantee that the Supreme Court will rule against the government.

How does an American who is labeled an enemy combatant ultimately get tried? Answer: he doesn’t. Under the Military Commissions Act, trial by military tribunal is limited to foreigners. So, even though Americans still have the use of habeas corpus (so far) to test whether their detention is lawful, if the Supreme Court ultimately upholds the “unlawful enemy combatant” designation for people accused of terrorism, Americans will be returned to indefinite military custody as “unlawful enemy combatants” if the government has provided some evidence of terrorism at the habeas corpus hearing.

The irony is that while foreigners will be accorded the kangaroo tribunal treatment, Americans accused of terrorism will continue to languish in military prison indefinitely without the benefit of a trial. Of course, given that the tribunals will have the power to impose the death penalty, Americans might do well not to complain about their indefinite detention.

Mr. Hornberger is founder and president of The Future of Freedom Foundation. He will be among the 22 speakers at FFF’s upcoming conference on June 1-4 in Reston, Virginia: “Restoring the Constitution: Foreign Policy and Civil Liberties” (www.fff.org/whatsNew/conference.htm). Send him email.