As publius noted, the Supreme Court has ruled in Boumedienne et al v. Bush (pdf). Herewith, a quick and dirty rundown of the issues. As befits someone with no legal training, I have stuck to the straightforward issues, leaving complexities to others (cough, publius, cough.) I'm basically trying to explain this to non-lawyers like myself.
Boumediene and the other petitioners are detainees at Guantanamo. They want to know: do they have the right to file a writ of habeas corpus -- that is, to ask the government to justify their detention?
There are two sources of habeas rights: the Constitution and statutes. Considering statutes first: the Court finds, not surprisingly, that the Military Commissions Act stripped Guantanamo detainees of all statutory habeas rights. That was one of its points, and it was why I was so opposed to it.
However, statutes have to accord with the Constitution, and the Constitution says (I.9): "The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it." That sounds pretty definitive: the Military Commissions Act contained no finding that the United States has been invaded, or is in the midst of a rebellion, nor is there any evidence that either condition obtains. So that settles the matter, right?
Well, no. To see why, note that what the Constitution says is that absent either condition, "The Privilege of the Writ of Habeas Corpus shall not be suspended". What, one might ask, is this privilege? Who enjoys it, and where, and in what circumstances? Plainly, if I were detained by the FBI here in Baltimore, I would be covered. Equally plainly, if some Chinese citizen were detained by the Chinese government in Beijing, she would not have, in virtue of that fact, the right to file a petition of habeas corpus in US court.
So here are two questions the Court needs to answer: who has habeas rights? And where do they extend? The court's answer to the first question (who?) is, basically: everyone has them. (Meaning: if you are detained by the US government, in circumstances in which habeas rights would normally obtain, your lack of citizenship is no obstacle.)
As for the second question (where?), the Court looks at its own precedents, which concern such fascinating questions as: to what extent does the US Constitution extend to territories and possessions? It also looks at the British common law from before the Constitution was adopted, to see what the framers of the Constitution and those who adopted it might have understood "the" Privilege of the Writ of Habeas Corpus to involve. Did it extend, say, to people detained by the British in India, which was not then part of the British empire? What about Ireland and Scotland? And so on and so forth. The Court concludes that these cases do not settle the issue one way or another.
The government argues that people detained in Guantanamo do not have habeas rights, because the US government does not have legal sovereignty over Guantanamo. (The lease agreement with Cuba apparently says that Cuba retains "ultimate sovereignty" over Guantanamo.) Petitioners argue that the US nonetheless exercises complete control over Guantanamo, and so habeas rights should extend there. The Court sides with the petitioners, and its language is quite striking:
"The Government’s view is that the Constitution had no effect there, at least as to noncitizens, because the United States disclaimed sovereignty in the formal sense of the term. The necessary implication of the argument is that by surrendering formal sovereignty over any unincorporated territory to a third party, while at the same time entering into a lease that grants total control over the territory back to the United States, it would be possible for the political branches to govern without legal constraint.
Our basic charter cannot be contracted away like this. The Constitution grants Congress and the President the power to acquire, dispose of, and govern territory, not the power to decide when and where its terms apply. Even when the United States acts outside its borders, its powers are not “absolute and unlimited” but are subject “to such restrictions as are expressed in the Constitution.” Murphy v. Ramsey, 114 U. S. 15, 44 (1885). Abstaining from questions involving formal sovereignty and territorial governance is one thing. To hold the political branches have the power to switch the Constitution on or off at will is quite another. The former position reflects this Court’s recognition that certain matters requiring political judgments are best left to the political branches. The latter would permit a striking anomaly in our tripartite system of government, leading to a regime in which Congress and the President, not this Court, say “what the law is.” Marbury v. Madison, 1 Cranch 137, 177 (1803).
These concerns have particular bearing upon the Suspension Clause question in the cases now before us, for the writ of habeas corpus is itself an indispensable mechanism for monitoring the separation of powers. The test for determining the scope of this provision must not be subject to manipulation by those whose power it is designed to restrain."
Or, in short: if we accept the government's argument, we would concede that it can legally do what it has tried to do in fact: to create a legal black hole in which it can act outside the law and the Constitution. We cannot do that.
This is, to my mind, the most important holding in the opinion. It defends the separation of powers against an attempt by the Executive to free itself from the constraint of law. That is immensely important.
There is a further question: granted that the detainees have habeas rights, they might not be entitled to a habeas petition now had they been afforded some procedure that was an adequate substitute for habeas proceedings. The Court would normally punt this one back to District Courts, but it declines to do so, on the grounds that due process for these detainees has already been delayed too long, and the separation of powers questions this issue raises are too important.
The Court says: the procedures provided under the Detainee Treatment Act are not adequate substitutes for habeas since (p. 60) "we see no way to construe the statute to allow what is also constitutionally required in this context: an opportunity for the detainee to present relevant exculpatory evidence that was not made part of the record in the earlier proceedings."
It's also worth noting that this decision was 5-4, with Roberts, Scalia, Thomas, and Alito in dissent. If Bush had been able to fill one more vacancy, and if he had (as he has in the past) chosen someone who shares the Cheney/Addington view of executive power, this decision would have come out differently. That is, to me, a terrifying thought. Because Publius' headline is accurate: with this decision, Court Reaffirms Existence Of Constitution. But had one vote changed, they would have given the Executive the power to avoid it at will.