Just got the CNN email alert which says:

The Supreme Court rules President Bush overstepped his authority with military war crimes trials for foreigners held at Guantanamo Bay in a case involving a former driver for Osama bin Laden.

No full story yet.  Obviously, I’ll be updating this….

UPDATE: Marty Lederman on what the Hamdan case is about:

There is little or no question about the constitutionality of the military commissions. (Although there is an outside possibility the Court will rule that the alien defendants are protected by the Due Process Clause (see footnote 15 of Rasul) and that the commissions fail to provide due process.)

Nor, in my view, is there any real question that Congress has as a general matter authorized the use of military commissions to try crimes against the laws of war. That was essentially the holding of cases such as Quirin and Yamashita, and subsequently Congress re-enacted 10 USC 821, without calling into question those decisions.

The questions in Hamdan are, instead, whether Congress has authorized the types of commissions that the President has created — i.e., whether the commissions, as presidentially authorized and as implemented, conform to statutory authority — and whether and to what extent these commissions violate any restrictions that the statutes expressly or implicitly impose.

The most important restriction is likely to be that the commissions must themselves comply with the laws of armed conflict (LOAC). (Several Justices pressed the SG on this point at oral argument, suggesting that if Congress authorized the military to convene trials for violations of the laws of war, surely Congress would have insisted that those trials themselves comply with the laws of war.)

And then the key question becomes what, exactly, the laws of armed conflict require with respect to such commissions, and whether these commissions meet those specifications. And in determining that question, most of the attention will likely be on Common Article 3 of the Geneva Conventions, which might apply here as a matter of treaty obligation (a question on which the DC Circuit split 2-1), and which in any event likely reflects the customary LOAC to which the commissions must adhere. (More on the importance of Common Article 3 here and here.)

UPDATE:  SCOTUSBlog gives the bottom line:

The Supreme Court ruled on Thursday that Congress did not take away the Court’s authority to rule on the military commissions’ validity, and then went ahead to rule that President Bush did not have authority to set up the tribunals at Guantanamo Bay, Cuba, and found the commissions illegal under both military justice law and the Geneva Convention. The vote was 5-3, with the Chief Justice not taking part.

The Court expressly declared that it was not questioning the government’s power to hold Salim Ahmed Hamdan "for the duration of active hostilities" to prevent harm to innocent civilians. But, it said, "in undertaking to try Hamdan and subject him to criminal punishment, the Executive is bound to comply with the Rule of Law that prevails in this jurisdiction."

That quotation was from the main opinion, written by Justice John Paul Stevens. That opinion was supported in full by Justices Stephen G. Breyer, Ruth Bader Ginsburg and David H. Souter. Justice Anthony M. Kennedy wrote separately, in an opinion partly joined by Justices Breyer, Ginsburg and Souter. Kennedy’s opinion did not support all of Stevens’ discussion of the Geneva Convention, but he did find that the commissions were not authorized by military law or that Convention.

The decision was 5-3 with Alito, Scalia, and Thomas being the dissenters.  The Chief Justice took no part because he dealt with this case as a lower court judge (but even if he had, it would only be 5-4).

MORE FROM SCOTUSBLOG:

Justice Breyer, joined by Ginsburg, Kennedy and Souter, wrote separately to answer the dissenters’ complaint that the ruling would hamper the President’s ability to deal with a new and deadly enemy.

Allow me to interrupt at this point to say that the dissenters (Alito, Scalia and Thomas) are wankers.

The Court’s conclusion, Breyer said, "ultimately rests upon a single ground: Congress has not issued the Executive a ‘blank check.’…Indeed, Congress has denied the President the legislative auhority to create military commissions of the kind at issue here. Nothing prevents the President from returning to Congress tgo seek the authority he believes necessary." The Breyer opinion included a mini-lecture on the virtue of presidential consultation with Congress, at least "where, as here, no emergency prevents" such consultation. "The Constitution places its faith in those democratic means. Our Court today simply does the same."

Tell it, Breyer.