Hearing that another misguided California convert had been charged with treason, I was reminded of the dissent in Hamdi v. Rumsfeld, where Justice Scalia -- joined by Justice Stevens -- staked out a position that would have granted even more rights than the majority's opinion did:
Where the Government accuses a citizen of waging war against it, our constitutional tradition has been to prosecute him in federal court for treason or some other crime. ... The Founders inherited the understanding that a citizen’s levying war against the Government was to be punished criminally. The Constitution provides: “Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort”; and establishes a heightened proof requirement (two witnesses) in order to “convic[t]” of that offense. Art. III, §3, cl. 1.
In more recent times, too, citizens have been charged and tried in Article III courts for acts of war against the United States, even when their noncitizen co-conspirators were not. For example, two American citizens alleged to have participated during World War I in a spying conspiracy on behalf of Germany were tried in federal court. See United States v. Fricke, 259 F. 673 (SDNY 1919); United States v. Robinson, 259 F. 685 (SDNY 1919). A German member of the same conspiracy was subjected to military process. See United States ex rel. Wessels v. McDonald, 265 F. 754 (EDNY 1920). During World War II, the famous German saboteurs of Ex parte Quirin, 317 U.S. 1 (1942), received military process, but the citizens who associated with them (with the exception of one citizen-saboteur, discussed below) were punished under the criminal process. See Haupt v. United States, 330 U.S. 631 (1947); L. Fisher, Nazi Saboteurs on Trial 80—84 (2003); see also Cramer v. United States, 325 U.S. 1 (1945).
The modern treason statute is 18 U.S.C. § 2381; it basically tracks the language of the constitutional provision. Other provisions of Title 18 criminalize various acts of warmaking and adherence to the enemy. ... The only citizen other than Hamdi known to be imprisoned in connection with military hostilities in Afghanistan against the United States was subjected to criminal process and convicted upon a guilty plea. See United States v. Lindh, 212 F. Supp. 2d 541 (ED Va. 2002) (denying motions for dismissal); Seelye, N. Y. Times, Oct. 5, 2002, p. A1, col. 5. ...
Several limitations give my views in this matter a relatively narrow compass. They apply only to citizens, accused of being enemy combatants, who are detained within the territorial jurisdiction of a federal court. This is not likely to be a numerous group; currently we know of only two, Hamdi and Jose Padilla. Where the citizen is captured outside and held outside the United States, the constitutional requirements may be different.