The United States Supreme Court has in a ruling struck down the military tribunal system set up to try Guantanamo prisoners.
The court said it will restore the judiciary to its rightful place.
The highest US court, by a 5-3 vote, declared that the tribunals that Bush created after the September 11 attacks violated the Geneva Conventions and US military rules.
The decision is seen as a stinging blow to the US administration in a case brought by Salim Ahmed Hamdan, who was Osama bin Laden's driver in Afghanistan.
Hamdan, who was captured in November 2001, is one of close to 500 foreign suspects at the US naval base in Guantanamo Bay, Cuba.