Can the president constitutionally declare war?

NPR -  Article I gives Congress the power "to declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water." Article II, meanwhile, designates the president as "Commander in Chief of the Army and Navy of the United States," giving the executive authority to direct the military once conflict has been authorized.

"I think it's pretty clear that the framers thought that any time we were going to be making the decision to go to war with another country, that was going to be a decision for Congress," says Rebecca Ingber, a law professor at Cardozo Law School in New York.

Yet presidents have long sent U.S. forces into combat without a formal declaration of war. As an early example of this, Stephen Griffin, a constitutional law professor at Tulane Law School, points to the Quasi War, a limited naval conflict between the fledgling U.S. and its erstwhile Revolutionary War ally, France. It took place at the end of the 18th century but there was never any formal declaration of war between the two countries.

That trend accelerated after World War II, driven by a combination of new military technologies and evolving global institutions.

"The creation of the atom bomb changed the game," says Griffin. In the early republic, communications were slow and military deployments took months. After 1945, however, "things were speeded up," Griffin notes. "You would need sometimes an instant response."

He also points to the influence of the United Nations, which the U.S. helped establish in 1945. The U.N. Charter prohibits the use of force by member states except in self-defense or with Security Council approval. Even in the U.S., that framework helped shift legal discussions away from formal declarations of war and toward concepts like "use of force," he says.

Critically, Griffin says, the Constitution doesn't require Congress to issue a formal declaration of war. What matters is legislative approval — such as an authorization for the use of military force (AUMF). "The constitutional requirement is about legislative approval," he explains, "not literally picking up a document that says, 'Declaration of War' and signing it."  More