The Bush administration has been a waging a fierce battle for the power to lock people up indefinitely simply on the president’s say-so. It scored a disturbing victory last week when a federal appeals court ruled that it could continue to detain Ali al-Marri, who has been held for more than five years as an enemy combatant. The decision gives the president sweeping power to deprive anyone — citizens as well as noncitizens — of their freedom. The Supreme Court should reverse this terrible ruling.

Mr. Marri, a citizen of Qatar legally residing in the United States, was initially arrested in his home in Peoria, Ill., on ordinary criminal charges, then seized and imprisoned by military authorities. The government, which says he has ties to Al Qaeda, designated him an enemy combatant, even though it never alleged that he was in an army or carried arms on a battlefield. He was held on the basis of extremely thin hearsay evidence.