The Bush administration's detention policies have been perhaps the most enduringly controversial aspect of its global war on terrorism.
About 600 detainees are being held in Guantanamo Bay
Now, these Supreme Court rulings are perhaps the most significant legal setback for the administration in the conflict.
Officially, the administration is taking its time to assess the rulings. But they certainly represent a political blow for the administration.
What they mean for the actual fate of the detainees isn't clear. That will depend on how the courts proceed from here.
The Supreme Court's decisions are not a comment on the guilt or innocence of the detainees.
But they're certainly going to open the floodgates for legal appeals. And for that reason their overall legal and political impact may also still have to be judged.
The Supreme Court has basically ruled that suspected terrorists or "enemy combatants", whether American or foreign, should at least have the right to a hearing in a US court, even if they're held at the detention centre at Guantanamo Bay.
The administration had contended is not sovereign US soil, and therefore not within the jurisdiction of US courts.
The American Civil Liberties Union called the rulings historic.
The first response from the US Department of Justice was that the Supreme Court had upheld the authority of the President to detain enemy combatants, including American citizens.
"This authority is crucial in times of war whether the enemy combatants are individuals who join our enemies on the battlefield to fight against America and its allies, or whether they are individuals who infiltrate our border to commit hostile and war-like acts against our nation," a Justice Department spokesman said.
But the court appeared to put restraints on that authority in time of war in a way which surprised some observers.
Traditionally, the Supreme Court has been reluctant to take such action.
As one of the justices, Sandra Day O'Connor, put it, they're a reminder that "a state of war is not a blank cheque for the president".
And, simply because of their timing, the Supreme Court rulings add to the impression of the Bush administration on the legal defensive.
The cases may not be related, but it has beaten a retreat at the United Nations on the issue of legal immunities for US troops serving abroad.
And its overall approach to the treatment of detainees is under a political microscope following the Abu Ghraib prisoner abuse scandal.