Lots of people hold similar views, but in fact the matter is not nearly so simple.
First, an excerpt from Article 1, section 8 of the U.S. Constitution. These are the powers of Congress with respect to the military:
To declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water;
To raise and support armies, but no appropriation of money to that use shall be for a longer term than two years;
To provide and maintain a navy;
To make rules for the government and regulation of the land and naval forces;
To provide for calling forth the militia to execute the laws of the union, suppress insurrections and repel invasions;
To provide for organizing, arming, and disciplining, the militia, and for governing such part of them as may be employed in the service of the United States, reserving to the states respectively, the appointment of the officers, and the authority of training the militia according to the discipline prescribed by Congress;
To exercise exclusive legislation in all cases whatsoever, over such District (not exceeding ten miles square) as may, by cession of particular states, and the acceptance of Congress, become the seat of the government of the United States, and to exercise like authority over all places purchased by the consent of the legislature of the state in which the same shall be, for the erection of forts, magazines, arsenals, dockyards, and other needful buildings;--And
To make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States, or in any department or officer thereof.
Sounds pretty clear so far, right? Now consider the legal history of the war powers clause above:
http://en.wikipedia.org/wiki/War_Powers_ClauseSometimes referred to as the War Powers Clause, the United States Constitution, Article One, Section 8, Clause 11, vests in the Congress the exclusive power to declare war.
Five wars have been declared in American history: the War of 1812, the Mexican-American War, the Spanish-American War, World War I and World War II. Some historians argue that the legal doctrines and legislation passed during the operations against Pancho Villa constitute a sixth declaration of war.
However, beginning with the Korean War, American presidents have not sought formal declarations of war, instead maintaining that they have the constitutional authority, as commander in chief (Article Two, Section Two) to use the military for "police actions".In 1973, Congress passed the War Powers Resolution, which requires the president to obtain either a declaration of war or a resolution authorizing the use of force from Congress within 60 days of initiating hostilities. Its constitutionality has never been tested as Congress has always passed the required authorization when requested by the president.
Some legal scholars maintain that all military action taken without a Congressional declaration of war (regardless of the War Powers Resolution) is unconstitutional; however, the Supreme Court has never ruled directly on the matter.
There is also much debate about the meaning of the word 'declare.' Some scholars suggest that to declare war does not necessarily mean to 'commence war.' During the Philadelphia Convention, there was some discussion about the difference between the power to 'make war' and the power to 'declare war,' and which of the two should be written into the Constitution. A declaration of war lets the citizens of a nation know that they are now at war with some other nation or entity. It also puts the belligerent nations and their citizens on notice. More importantly, this establishes that the 'law of nations' or international law is governing the conduct of war. This protects citizens in all the warring nations involved insofar as if they are captured by the enemy, they will be treated as prisoners-of-war instead of mere criminals.
In essence, Congress has agreed that it can "authorize" the president to "conduct wars" in the absence of a formal declaration-- it has agreed to a disinction between "making war" and "declaring war." Presidents have ALWAYS argued that Article Two gives them this authority as Commander in Chief of the military, i.e. sole authority about how the military is used is vested in the president. (on edit-- an interesting aside to this is that it makes it entirely possible for congress to declare a war that the president refuses to fight-- as CinC he has the ability to simply not engage an enemy despite a congressional declaration-- unlikely, but there it is.) Congress tried to seal this loophole in 1973 with the War Powers Resolution, which every president since Nixon has held to be unconstitutionally limiting of presidential powers, but which has the (perhaps) unintended side effect of providing a formal mechanism for presidents to go to war without a congressional declaration.
http://en.wikipedia.org/wiki/War_Powers_ResolutionProvisions
The purpose of the War Powers Resolution is to ensure that Congress and the President share in making decisions that may get the U.S. involved in hostilities. Portions of the War Powers Resolution require the President to consult with Congress prior to the start of any hostilities as well as regularly until U.S. armed forces are no longer engaged in hostilities (Sec. 3); and to remove U.S. armed forces from hostilities if Congress has not declared war
or passed a resolution authorizing the use of force within 60 days (Sec. 5(b)). Following an official request by the President to Congress, the time limit can be extended by an additional 30 days (presumably when "unavoidable military necessity" requires additional action for a safe withdrawal.
History
Under the Constitution, war powers are divided. Congress has the power to declare war and raise and support the armed forces (Article I, Section 8), while the President is Commander in Chief (Article II, Section 2). It is generally agreed that the Commander in Chief role gives the President power to repel attacks against the United States and makes him responsible for leading the armed forces. During the Korean and Vietnam wars, the United States found itself involved for many years in undeclared wars. Many Members of Congress became concerned with the erosion of congressional authority to decide when the United States should become involved in a war or the use of armed forces that might lead to war. The Senate and the House of Representatives achieved the 2/3 majority required to pass this joint resolution over President Nixon's veto on November 7, 1973.
(snip)
After combat operations against Iraqi forces ended on February 28, 1991, the use of force to obtain Iraqi compliance with U.N. resolutions remained a War Powers issue, until the enactment of P.L. 107-243, in October 2002, which explicitly authorized the President to use force against Iraq, an authority he exercised in March 2003, and continues to exercise for military operations in Iraq. Congress had the authority to debate a declaration of war against Iraq and decline to do so-- that would have removed ANY political cover from what is undoubtedly a crime against humanity under international law. It could also have declined to give the authority to use force under the War Powers Resolution, with the same effect. Make no mistake, Bush would have undoubtedly invaded anyway citing his Article Two authority and simply returned to Congress to seek further authorization after 60 days-- this is not a congress that seems much inclined to deny him anything. Instead, congress gave away the house with barely a whimper, and gave the Bush administration complete legal cover UNDER U.S. LAWS for waging a war of aggression against Iraq. That means that successful U.S. prosecution will be that much more difficult-- congress gave the Bush administration a get-out-of-jail-free card for at least the war crime of an unprovoked war of aggression.
It's disingenuous in the extreme to suggest that the IWR was "not authorization to invade Iraq." Under the WPR Bush did not actually need any authorization to invade Iraq, but had congress denied him the IWR it would have had some recourse for stopping it or for holding him responsible.