Congress may not be able to give Bush military commissions to try Guantanamo Bay detainees without derogating from the Geneva Conventions (1949). Yet the scope of the jurisdiction of military commissions stems from the battlefield necessity of trying crimes of war--exactly the sort of thing defined in the Conventions and other international treaty obligations. Such logical inconsistency will invite further judicial review.
In Hamdan v Rumsfeld (2006) the US Supreme Court stated: (1) military commissions set up by the executive without congressional action were ultra vires; (2) that the detainees at Guantanamo Bay and other sites were covered by Art. 3 and, possibly, Art. 1 of the Geneva Conventions; and (3) Congress could, within certain limits, authorize such tribunals.
Art. 3(1)(d) of the Geneva Conventions (1949) reads in part: "The passing of sentences and the carrying out of executions without previous judgment pronounced by a regularly constituted court affording all the judicial guarantees which are recognized as indispensable by civilized peoples." Since the original military commissions were creatures of the executive branch only, they failed the "regularly constituted court" test. Within the scheme of the Conventions, a violation of Art. 3 counts as a war crime, and domestic law gives effect to the treaty provisions.
So the next question is: in what instances can Congress create a "regularly constituted" military commission? There is some guidance in Section V of Justice Stevens's opinion. Historically, military commissions appear in three situations: (a) during times of martial law; (b) for trial of government officials on enemy territory when the civil government is not functioning; and (c) for tial of offences "incident to the conduct of war." What (a)-(c) have in common is that that they try offences outside the usual jurisdiction of the domestic courts, e.g., offences not in US territory or where a civil jurisdiction has ceased to function.
To be consistent with precedent and not invite judicial review Congress would have to authorize military commissions of class (c) that try offences: (i) committed post 9/11; (ii)in the theater of war; and (iii)which are violations of internationally recognized rules of warfare. Thus, for example, such a commission would be incompetent to try Hamden for his pre-9/11 activities or on his current charge of conspiracy since that offence is unknown as a war crime.
Further, the rules of evidence in the Congressionally-mandated miliary commissions will have to parallel those in civil courts or courts-martial if the "regularly constituted court" test is to be satisfied. Ordinary evidence rules will exclude information obtained by harsh interrogation techniques and require disclosure of the sources of information obtained in intelligence-gathering operations. Here tainted evidence will further limit the pool of triable cases, perhaps foreclosing the possibility of successful prosecutions entirely.
So Congress might well find itself in the position of a mountain in labor giving birth to a mouse as it attempts to fashion Art. 3 compliant military commissions for the detainees. On the other hand, should it attempt to suspend Art. 3 protections, then the result would be self-stultifying, i.e., a Geneva-Convention-violating court constituted to try war crimes. The easier path through Justice Stevens's obstacle course is to do what should have been done in the first place: give the detainees trials in the domestic courts or in courts-martial.