The Supreme Court ruled Thursday that President Bush overstepped his authority in creating military war crimes trials for Guantanamo Bay detainees, a rebuke to the administration and its aggressive anti-terror policies.
Justice John Paul Stevens wrote the opinion, which said the proposed trials were illegal under U.S. law and the Geneva Convention.
The case, one of the most significant involving presidential war powers cases since World War II, was brought by Guantanamo prisoner Salim Ahmed Hamdan, who was a driver for Osama bin Laden in Afghanistan.
The vote was split 5-3, with moderate Justice Anthony M. Kennedy joining the court's liberal members in ruling against the Bush administration. Chief Justice John Roberts, named to the court last September by Bush, was sidelined in the case because as an appeals court judge he had backed the government over Hamdan.
Thursday's ruling overturned that decision.
After the Sept. 11 attacks, Bush established special war crimes tribunals for trying prisoners held at the U.S. military base at Guantanamo Bay in Cuba.
Of about 450 prisoners at Guantanamo, only Hamdan and nine others face charges before a tribunal. Human rights groups have criticized the tribunals, formally called military commissions, for being fundamentally unfair.
Hamdan's lawyers had challenged Bush's power to create the tribunals and said he is covered by the Geneva Convention, and therefore rules governing U.S. courts-martial should be applied.
The ruling was eagerly awaited by Bush administration officials, who want to bring charges against more prisoners, and by groups like Human Rights Watch, which has called on Bush to close Guantanamo.
The ruling only addressed the military tribunals, not broader issues such as whether the base should be closed.
At a news conference in Vienna last week, Bush said he was awaiting the Supreme Court's ruling before deciding the proper forum to try Guantanamo prisoners.
In its other rulings on Bush's policies in the war on terrorism, the Supreme Court issued a pair of decisions two years ago that placed limits on the president's powers and allowed Guantanamo prisoners to bring lawsuits in U.S. courts.