Civil right groups on Thursday hailed a Supreme Court decision on military tribunals at Guantanamo Bay as a major victory for the rule of law and a slap in the face for President George W Bush.
Official reaction was muted; with Bush saying the ruling required further study while stressing adding that his administration would take the court's findings "seriously."
In a 5-3 vote, the Supreme Court ruled that Bush had overstepped his powers in setting up military war crimes tribunals for detainees at Guantanamo Bay in Cuba.
"This decision moves us one step closer to stopping the abuse of power that has become the hallmark of this White House," said Anthony Romero, executive director of the American Civil Liberties Union (ACLU).
Specifically, the court said the administration violated the Geneva Conventions and the US military code of justice in ordering a military tribunal to prosecute Salim Ahmed Hamdan, a Yemeni former driver for Al-Qaeda leader Osama bin Laden.
The ruling could have far-reaching consequences for all the estimated 450 Guantanamo detainees, as well as the general conduct of the US "war on terror."
"The Supreme Court has made clear that the executive branch does not have a blank check in the war on terror and may not run roughshod over the nation's legal system," Romero said.
Speaking to reporters outside the Supreme Court building, Hamdan's military-appointed attorney, Lieutenant Commander Charles Swift, said the ruling marked a "high water point" in American history.