Prof. John Yoo endorses the Obama Administration's argument that it already has authority to make war on ISIS. As Prof. Ilya Somin notes, there are a number of flaws with that argument. One thing I'll add: the AUMF does not authorize the President "to take action to deter and prevent acts of international terrorism against the United States." It just says that the Constitution gives the President that authority. But it does not specify what exactly such authority encompasses. This is a significant difference. If I say that a baker already is capable of making desserts, that does not mean that he has the ability to make a particular pie in a particular way. And if the Constitution does not give the President that authority, then the AUMF certainly can't give it to him. So the AUMF only reiterates (or purports to reiterate) what power the President already enjoys.
Yoo does not claim otherwise: he invokes the AUMF, not as legally binding, but as proof that Congress, at one time, agreed with his broad interpretation of Constitutional power. Still, I think it's too much to say that the phrase "take action to deter and prevent acts of international terrorism against the United States" includes a constitutional "power...to attack countries and terrorist groups to prevent them from harming the U.S., even if not with an imminent attack." Everyone believes that the President has the power to "take action to deter and prevent acts of international terrorism" at some point. Nobody thinks that he can only act after a bomb explodes. But whether this indefinite "action to deter" also includes the "power...to attack countries" that are not threatening the United States with imminent attack...well, that's a highly dubious proposition.
Does the Constitution give the President power "to attack countries" that are "not [threatening the U.S.] with an imminent attack"? That seems like a very extreme proposition, and requires extreme proof. The Constitution's authors were well versed in the history of the Stuart Monarchy, among whose crimes was waging war without Parliamentary approval. That crime was one of the leading reasons for the English Civil War and the later Glorious Revolution, two events that laid the intellectual framework for the American Revolution. The idea that the American founders meant to restore the British Monarchy in the form of the American President is simply laughable. And the idea that the AUMF's reference to "action to deter and prevent attacks" includes absolutely limitless Presidential authority is plainly contrary to every principle of American constitutionalism.
Such a notion was expressly rejected by, among others, James Wilson. Wilson (signer of both the Declaration and the Constitution, and second only to James Madison as the Convention's most important delegate) distinguished the American presidency from the British monarchy on just this point: "As the law is now received in England, the king has the sole prerogative of making war. On this very interesting power, the constitution of the United States renews the principles of government, knnown in England before the conquest [of 1066]." In other words, the Constitution denies the President the "sole prerogative of making war."
At the time Wilson was writing, it was generally believed that the more expansive understanding of British monarchical power had begun only after the Norman Conquest. This theory, today called Whig History, is largely rejected today, but Wilson believed it. He believed that "the chief difference between the Anglo-Saxon and the Anglo-Norman government" was that in the former, the power to make war had been considered legislative, while "in the latter, it was transferred to the soveriegn." Thus there was "a pleasure in reflecting on" the fact that the American Constitution was a "renovation of the ancient constitution of England.... [O]ur national government is recommended by the antiquity, as well as by the excellence, of some of its leading principles." 2 Collected Works of James Wilson 871 (K. Hall & M. Hall, eds. 2007)
Also, the distinction between "making" and "declaring" war, on which Yoo rests much of his argument, is also unpersuasive. Note this exchange at the Constitutional Convention:
Mr. Madison and Mr. Gerry moved to insert "declare," striking out "make" war; leaving the Executive the power to repel sudden attacks.
Mr. Sharman though it stood very well. The Executive shd be able to repel and not to commence war. "Make" better than "declare" the latter narrowing the power too much.
Mr. Gerry never expected to hear in a republic a motion to empower the Executive alone to declare war.
Mr. Elsworth. there is a mterial difference between the cases of making war and making peace. It shd. be more easy to get out of war, than into it. War also is a simple and overt declaration, peace attended with intricate & secret negociations.
Mr. Mason was agst. giving the power of war to the Executive because not safely to be trusted with it; or to the Senate, because not so constructed as to be entitled to it. He was for clogging rather than facilitating war; but for facilitating peace. He preferred "declare" to "make."
On the motion to insert declare--in place of make, it was agreed to.
Note that while the delegates did replace "make" with "declare," they did so for the opposite reason that Yoo claims: Madison and Gerry's motion was designed to allow the President to repel sudden attacks, and while every delegate who spoke on the question insisted that the President should not be able to start a war on his own, nobody spoke to the contrary in support of a unilateral presidential authority to commence war. There is thus no evidence that the distinction between "making" and "declaring" war was intended (by the Philadelphia delegates) for the purposes assumed by Yoo's argument.
This does not prove that the AUMF doesn't authorize attacking ISIS. In fact, as I've argued, if the President can demonstrate that ISIS is an organization that "planned, authorized, committed, or aided the terrorist attacks that occurred on September 11," or that "harbored" those who did, or that it is composed of "persons" who did any of these things, then the AUMF does indeed authorize war on ISIS.