The US Supreme Court today ruled the military tribunal for Guantanamo prisoner Salim Ahmed Hamdan lacks the power to proceed because it violates the Geneva Conventions.
But experts agree that while the ruling is an embarrassment for the Bush administration, it may have little immediate effect on future the detention camp that holds 450 foreign captives at a US naval base in Cuba.
An all terrain vehicle passing by the entrance to Camp Delta 4 prison, at Guantanamo
The court upheld today a Guantanamo detainee's challenge to President Bush's power to create the military tribunals to try suspected al-Qaeda conspirators and Taliban supporters after the September 11th attacks.
In a major defeat for Mr Bush, the court found he had overstepped his presidential powers in creating the tribunals. The arrest and detention without trial of terrorist suspects has been condemned by human rights groups, the United Nations and foreign governments.
The tribunals have also drawn condemnation from lawyers, who say they are rigged to ensure conviction and offer none of the basic guarantees and rights granted suspects in the US justice system or to which formal prisoners of war would be entitled.
Ten detainees at Guantanamo have been charged before the tribunals, and prosecutors had intended to charge as many as 25 more before today's ruling.
"We conclude that the military commission convened to try Hamdan lacks power to proceed because its structure and procedures violate the international agreement that covers treatment of prisoners of war, as well as US military laws," Justice John Paul Stevens wrote.
That part of the decision was a serious blow for the administration in a case brought by Mr Hamdan, who was Osama bin Laden's driver in Afghanistan.
The White House declined to comment until after the court's 5-3 decision was studied.
While the decision has no direct bearing on the future of the controversial detention centre, legal and security experts say it has indirectly strengthened the hand of those demanding it be closed.
Scott Silliman, a retired Air Force attorney who is now executive director of Duke University's Centre on Law, Ethics and National Security in North Carolina, said that while the ruling only affected the 10 men charged, it reopened the question of what to do with the 440 others.
Retired Air Force lawyer, Lt Col Jeffrey Walker said the administration was asserting an "incredibly broad executive authority" which was "very nebulously defined"
"This is nothing but a slap in the face of the administration," Lt Col Walker said and he speculated that there would be further legal challenges.
The decision quickly triggered calls by critics such as the American Civil Liberties Union, which said "the president should make good on his promise and close Guantanamo."
"My suspicion is that the whole future of the Guantanamo structure is now in some turmoil," said Michael Krauss, a law professor at George Mason University in Virginia.
Mr Krauss called the ruling a "devastating defeat for the administration."
Todd Gaziano, a Supreme Court expert at the conservative Heritage Foundation, said the ruling placed inappropriate limits on executive authority said it was "a historical disgrace on the court.".
"It is profoundly disturbing that the court would take away from the commander-in-chief the sole discretion of determining what is militarily necessary."
But he said the decision would not have a major impact on the president's ability to wage the war against terrorism, since he could still resort to other procedures not denied by the court. Congress could also "fix the errors that the court has read into the treaties and statutes," he added.