Extremely heated debate developed in the United States beginning on or around September 11, 2001. Opponents of the uses of military force since began to argue, chiefly, that the Iraq War was unconstitutional, because it lacked a clear declaration of war, and was waged over the objection of a significantly sized demographic in the United States.
Instead of formal war declarations, the United States Congress has begun issuing authorizations of force. Such authorizations have included the Gulf of Tonkin Resolution that greatly increased American participation in the Vietnam War, and the recent "Authorization of the Use of Military Force" (AUMF) resolution that started the War in Iraq. Some question the legality of these authorizations of force. Many who support declarations of war argue that they keep administrations honest by forcing them to lay out their case to the American people while, at the same time, honoring the constitutional role of the United States Congress.
Those who oppose requiring formal declarations of war argue that AUMFs satisfy constitutional requirements and have an established historical precedent (see Quasi-War). Furthermore, some have argued that the constitutional powers of the president as commander-in-chief invest him with broad powers specific to "waging" and "commencing" war.
The February 6, 2006, testimony of Alberto Gonzales to the U.S. Senate Judiciary Committee Hearing on Wartime Executive Power and the National Security Agency's Surveillance Authority, however indicates otherwise:
GONZALES: There was not a war declaration, either in connection with Al Qaida or in Iraq. It was an authorization to use military force. I only want to clarify that, because there are implications. Obviously, when you talk about a war declaration, you're possibly talking about affecting treaties, diplomatic relations. And so there is a distinction in law and in practice. And we're not talking about a war declaration. This is an authorization only to use military force.