With recent polls showing Americans beginning to turn against the war in Afghanistan, and U.S. military leaders saying that the Taliban is gaining, rather than losing strength, the Obama Administration has reason to worry about the possibility of a substantial gap between the troop levels the public will support and the troop levels needed to defeat the insurgency (assuming it can be defeated). These issues of politics and military tactics go beyond my expertise as a constitutional lawyer, although I have views about them as a citizen.
Here I want to raise what is at least partly a legal question: At what point, if any, will the war cease to be legally authorized? There is an international dimension and a domestic dimension to that question. As a matter of international law, the U.S. (joined by NATO allies) justified its attack on the Taliban government of Afghanistan in late 2001 as self-defense in response to 9/11 and the Taliban's refusal to turn over its Al Q'aeda perpetrators. At the time that rationale probably satisfied U.N. Charter Article 51's recognition of the inherent right of individual and collective self-defense.
Even if that justification eventually expires simply via the passage of time, we are still close enough to the original events, and the Taliban and Al Q'aeda still pose a sufficient threat, to warrant a continued troop presence, although this is complicated by at least two factors. First, the continued presence of Western troops in Afghanistan may well be fueling the Taliban insurgency, at least over the long run. Second, from some point after the Taliban was overthrown (shortly after the invasion), Afghanistan has had a friendly government. The original warrant for war does not run against the current government (regardless of which non-Taliban candidate ends up winning the election). But because the current Afghan government welcomes NATO troops, we need not worry too much about whether those troops would be in violation of international law were they to remain against the will of the current government.
So let us turn to domestic law. Here it may be instructive to note that more time has elapsed since Congress enacted the Authorization for Use of Military Force (AUMF) of Sep. 18, 2001, than elapsed between the passage and repeal of the Tonkin Gulf Resolution. President Nixon did not end the war in Vietnam in response to that repeal, but he had at least the fig leaf of an argument: Because the U.S. was slowly drawing down troops, Nixon said that as Commander in Chief, he had the inherent power to ensure their safety in the process. By contrast, if Congress were to repeal the AUMF, President Obama, who is maintaining or increasing troop levels, could not make the same claim.
Of course, Congress is not likely to repeal the AUMF, at least not yet. But the AUMF could eventually expire on its own. Here the considerations are slightly different than in the international sphere. The cause that justified force under UN Charter Article 51 might persist for decades, thus justifying--as a matter of international law--continued troop presence for that long. But domestically, the issue is less a matter of whether military force is justifiable than it is whether the use of military force has received democratic consent. The Constitution places the power to declare War in Congress, the usual account goes, because Congress will not lightly take the country to war. Extrapolating, we might well conclude that at some point the mere passage of time DOES count as vitiating the public consent to war.
Have we reached that point? I don't think so. I also acknowledge that no court is likely to rule on these matters. And while I think it would be best if Congress itself took the initiative to revisit declarations of war (or their equivalents) every few years, there are structural reasons why that won't happen until long after public opinion has turned decisively against a war. (I discussed some of these in 2002 here.)
Finally, and to be clear, I want to reiterate that I do not have a strong view about what the most sensible long-term strategy is with respect to Afghanistan (or Iraq for that matter). I do think that domestic public opinion--and thus our system of checks and balances--could eventually constrain the available options quite severely.
Posted by Mike Dorf