The Constitution gives Congress the power to declare wars, fund them, and oversee the way they are fought. Yet the Constitution never says exactly how these powers are to be reconciled with the president's authority as commander in chief. The Constitution surely must empower the president to fight wars effectively enough to win them. That means that war must be conducted under the president's direction, not run by committee. In the modern era, no country—not even a parliamentary democracy—has been so foolhardy as to place a war under the guidance of a legislative body, rather than a single, unified command....Read the whole thing.
The short answer to the question of institutional competence is that Congress is good at expressing the popular will about whether we should be at war or not, and what kind of a war it should be, while the president is good at actually fighting the war (or at least he should be). The Constitution should therefore be understood to allow Congress to declare and define the nature of the war while guaranteeing the president's authority to make decisions that are crucial to the tactical conduct of it.
March 6, 2007
Noah Feldman and Samuel Issacharoff explain why Congress lacks the power to manage the war: