Proponents of extreme executive power are aided in their project by an unlikely ally - nine-tenths of the U.S. Senate
Without any approval from Congress, presidents have sent forces to battle Indians, Barbary Pirates and Russian revolutionaries, to fight North Korean and Chinese Communists in Korea, to engineer regime changes in South and Central America, and to prevent human rights disasters in the Balkans. Other conflicts, such as the 1991 Persian Gulf War and the 2003 Iraq War, received legislative "authorization" but not declarations of war.
~ John Yoo, writing in The Wall Street Journal
This defense of President Obama's behavior in Libya is the one that most amuses me, especially when it is made by conservatives who believe that ever since the New Deal the executive branch has been defiling the memory of the Founders. They'll insist that the federal government has been in violation of the commerce clause, properly understood, for many decades now. Change the subject to war, however, and the fact that American presidents have waged it in the past without Congressional authorization is taken as proof that the practice is constitutionally sound.
Writing on this subject in Ricochet, Richard Epstein affirms the fact that Congress must authorize war, but adds this accurate addendum: "It will be harder and harder to insist that Congress has an essential place in the constitutional scheme unless it insists on it. It is not likely that courts will ever tiptoe into this arena, so that if the Congress does not stand up for itself, no one else would stand up for it."