Picking up on the thread that Tim began and that Peter and David have advanced, I wonder if we might gain some insight by looking at the other incorporation debate that occurred during the twentieth century—the debate over which provisions of the Bill of Rights should be applied to the states through the Fourteenth Amendment. I claim no particular expertise on that subject, but my recollection is that Justice Black thought the whole package should be applied wholesale, while Justice Harlan would have proceed provision by provision and applied only those that were most fundamental. If one compares Black’s and Harlan’s opinions in Reid, the parallels are obvious.
Justice Kennedy picked up Harlan’s position in Verdugo and essentially repeats it in Boumediene. Under this approach, certain rights like due process may apply everywhere the government acts (though I suppose what process is due might well vary, just as it does domestically), while others that are seen more as particularities of American law (e.g. the warrant requirement) are not.
In the domestic incorporation debate, the Supreme Court did proceed provision by provision (Harlan’s approach), but ended up incorporating almost all of the Bill of Rights (Black’s result). My memory is that only indictment by a grand jury and the right to a civil jury trial have not been applied to the states. I am not suggesting that the result will be or should be the same in the international context. Differences in legal culture may mean that what would be considered fundamental within the United States (a jury in criminal cases) might not be considered fundamental outside it (in Puerto Rico). But the basic question—is the right sufficient fundamental—may be the same.
But by what metric do we judge that question? Do we look to the legal traditions of other nations to find common ground, or is it up to the intuitions of the justices of the Supreme Court? Judging from Boumediene, the answer would seem to be the latter. There is perhaps no right more fundamental in Anglo-American law than habeas corpus (it was one of the few written into the original Constitution), but I believe it is largely unknown outside legal systems descended from England’s.