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. Where the exigencies of war prevent that, the Constitution's Suspension Clause, Art. I, §9, cl. 2, allows Congress to relax the usual protections temporarily. Absent suspension, however, the Executive's assertion of military exigency has not been thought sufficient to permit detention without charge. No one contends that the congressional Authorization for Use of Military Force, on which the Government relies to justify its actions here, is an implementation of the Suspension Clause.
The exceedingly important question before us is whether the President of the United States possesses the authority to detain militarily a citizen of this country who is closely associated with al Qaeda, an entity with which the United States is at war;