Historical practice, or custom, has long been seen as a source of authority in the resolution of separation-of-powers disputes. (1) In two recent cases assessing the limits to the president's power regarding the recognition of foreign nations (2) and the making of recess appointments, (3) the Supreme Court heavily emphasized past practice. Historical practice, the Court said, reflects "the compromises and working arrangements that the elected branches of Government themselves have reached." (4) In the realm of war powers, the executive branch has long relied on custom to justify military initiatives that were carried out without congressional approval. (5) In essence, the executive has argued that because force has been used in the past without congressional approval, the same is permissible in various other situations (for example, in the Dominican Republic, Grenada, Haiti, Kosovo, and Panama). (6)
The Obama administration has insisted that significant use of force without congressional approval is constitutionally permissible because of "the 'historical gloss' placed on the Constitution by two centuries of practice." (7) The administration made this claim explicitly to justify the use of force against Libya. (8) "Our history," it asserted, "is replete with instances of presidential uses of military force abroad in the absence of prior congressional approval." (9) The administration later claimed authority to use force against Syria (10) without congressional approval, and also against ISIS. (11) The administration has not provided--and Congress has not demanded--a formal legal opinion explaining its assertion of authority with respect to either of these latter two situations, but it is reasonable to infer that its rationale in both would again rest in part (12) on the probative value of historical practice.
This actual historical record suggests that reliance on past practice in the war powers realm is misplaced. Much of the difficulty can be capsulized in one word--incommensurability. Custom is properly established inductively by lining up historical precedents that are alike, disregarding precedents that are not alike, and then inferring a pattern of practice. The probity of the product--in constitutional law, as in other legal regimes in which custom serves as a source of authority--thus lies in ensuring that constitutive historical precedents are actually on point. Genuine precedents must be apposite, comparable in all important respects to the facts at hand. The problem in the realm of war powers is that three highly pertinent contextual factors undermine the commensurability of putative historical precedents: risk, emergency, and the congressional posture. The exclusion of data concerning these three elements renders customary methodology in the war powers realm excessively malleable, systematically favoring executive power over congressional power. (13) Assessments of historical war powers practice must therefore be viewed with skepticism.
Custom, moreover, does not stand alone as a source of authority in resolving separationof-powers disputes. The Court has recently given increased weight to functional considerations--that is, to a political branch's institutional characteristics that counsel for or against a role in certain types of decisions. Privileging war-powers historical practice, however, undervalues Congress's functional attributes in war-powers decision making and overvalues those of the executive. An elaboration follows.
The most important consideration in using force--and the one most often concealed if not disregarded in the list-making of incidents--concerns risk, or the level of danger created by the use of force in a given military operation. The Congressional Research Service acknowledges that it makes no effort to assess the magnitude of force employed in the U.S. military actions that it lists. (14) Nor does it purport to assess the risk that each such use of force entailed--including the gravity of the threat of retaliation against potential U.S. military targets beyond the battlefield, of the danger posed to noncombatants in the United States and elsewhere, of the peril of creating safe havens for groups hostile to the United States and its allies, of the likelihood of stoking regional antagonisms and instability, of the damage inflicted on the nation's worldwide reputation, and of the possibility of unintended consequences generally. Typically, reliance on custom tends to obscure known, foreseeable risks that were incurred at the time of a given action; it focuses instead on acontextual similarities among the catalogued incidents that are easily quantified afterwards but had little to do with initial risk. Inductively arrived-at formulae reflect the narrowness of that methodology. An example is the recurring reference by the Office of Legal Council...