In the Wall Street Journal, David B. Rivkin Jr. and Lee A. Casey: Congress Declares War, but Only the President Can Make It. From the introduction:
House Democrats, joined by a few Republicans, responded to the killing of Iran’s Maj. Gen. Qasem Soleimani by questioning the president’s authority to order that strike. But the resolution they passed last week makes a mockery of Congress’s own powers. It purportedly “directs the President to terminate the use of United States Armed Forces to engage in hostilities in or against Iran or any part of its government or military” unless Congress authorizes the use of force or an Iranian attack on the U.S. is “imminent.” But it’s styled as a nonbinding resolution. That means it doesn’t need Senate approval, but it also makes no pretense of having the force of law.
Which is just as well. Congress cannot limit the president’s constitutional authority to wage war in the way it pretends to here.
And from later on:
It’s true that the Constitution assigns Congress the power “to declare war.” Yet even in the 18th century, a declaration of war wasn’t required to create a state of armed conflict, governed by the laws of war. Today, such a declaration has to do with how citizens and property from belligerent and neutral states are treated, rather than the actual use of force. The last time Congress formally declared war was in 1942. Since World War II, lawmakers have approved U.S. military actions by other means, from the 1964 Gulf of Tonkin Resolution, which allowed President Lyndon B. Johnson to expand U.S. involvement in Vietnam, to the Authorization for Use of Military Force Against Iraq Resolution of 2002.
The power to declare war is different from the power to make war, which belongs to the president in his role as “commander in chief of the Army and Navy of the United States.” There are few constraints on that power when the president is defending Americans, civilian or military, against armed attack.
Even if it passes legislation, Congress cannot dictate when and how the president exercises his power over the military forces it has provided—especially in selecting targets.
I partly agree but mostly don’t. I agree that in an authorized war Congress cannot give tactical directions to the President. (discussed here). And I agree that absent a congressional prohibition, the President can respond to attacks (and highly imminent attacks) (discussed here and here). But (contrary to the linked post), I see the core of the declare war clause to be a prohibition on Presidents initiating war. (discussed here and at greater length in The Constitution’s Text in Foreign Affairs).
The difficult question is whether Congress can prohibit a military response when the President would otherwise have independent authority to respond. I’m inclined to think Congress has this power, as necessary and proper to its declare war power — to preserve its power to decide when and whether a war should start or continue. In any event, it seems clear that Congress could prohibit expenditures on military responses, including against specific countries.
NOTE: This post was originally published at The Originalism Blog, “The Blog of the Center for the Study of Constitutional Originalism at the University of San Diego School of Law,” and is reposted here with permission from the author.