The Congress shall have power…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…

— Constitution of the United States of America; Article I, Section 8

The President shall be commander in chief of the Army and Navy of the United States, and of the militia of the several states, when called into the actual service of the United States…

— Constitution of the United States of America; Article II, Section 2

In a televised address to the nation tonight, President George W. Bush is expected to call for a “surge” of troops into Iraq. Senator Edward Kennedy of Massachusetts, among others, opposes a surge, and wants Congress to pass legislation forbidding any increase in troop levels in Iraq. Our nation is about to embark on what could become a very contentious debate concerning the degree to which Congress can make tactical military decisions once a shooting war is underway.
1. Let’s dispose of two extreme poles right away. By the letter of the Constitution and by custom, Congress has the power to do more than simply fund the military and declare war. Consider for example, issues like base-closings or weapons-system acquisition. Congress has never in history said to the executive branch, here’s the money for the army, spend it any way you want. But there are limits to how far Congress can use its power “to make rules for the regulation of land and naval forces”. Does anyone think that Congress had a legitimate right to say in 1944, “We don’t think that landing you’re planning for Omaha beach this week is a good idea; the weather is too bad, so we’re cutting off funds for any operations except a landing at Utah beach next week”? Commander-in-Chief is more than a ceremonial title.
2. However much latitude the President has to act in his role as Commander-in-Chief during peacetime, he has even more during a declared war. That’s part of what a declaration of war fundamentally is, a broad grant of authority from Congress to the President, instructing him to use all resources available to defeat a foreign enemy, hopefully as quickly and efficiently as possible.
This separation between who declares a war and who carries it out is part of the genius of the American constitutional system. The Founders designed most government processes not to be efficient, but to slow things down. However, the Founders also realized that there would be circumstances — most notably confronting violent foreign powers — when decisions would have to be made faster than the deliberative process of Congress would allow. So they created a mechanism (the declaration of war) by which Congress could temporarily increase the power of the executive and made it clear (by designating the President Commander-in-Chief) that the executive was solely responsible for certain decisions until the war was done.
3. Furthermore, the Iraq War Resolution of 2002 explicitly gave the President wide latitude in prosecuting a war in Iraq…

The President is authorized to use the Armed Forces of the United States as he determines to be necessary and Appropriate in order to–
(1) defend the national security of the United States against the continuing threat posed by Iraq; and
(2) enforce all relevant United Nations Security Council resolutions regarding Iraq.

4. Trying to limit troops now would seem to be in contravention of the broad grant of power that Congress already gave the President in 2002. Can Congress contradict itself like that? Legalistically, yes. They only need to write one of those “notwithstanding any other legislation” clauses into a future bill that limits troop deployment or funding.
5. More importantly, the Iraq war resolution can be overridden by subsequent legislation because an “authorization to use military force” is something less than a full-out declaration of war. Congress cannot simply undeclare a war after declaring one. Wars can only end when both sides mutually agree to stop fighting, sometimes with one side surrendering to the other. The same is not true of an “authorization to use force”. An authorization to use military force can be rescinded without a surrender occurring or a treaty being signed.
6. This is good news for the anti-war folks. The distinction between a declaration of war and an authorization to use military force gives them the out they are looking for. The anti-war crowd wants to force what is in effect a surrender, but not accept responsibility for it. Because war was never formally declared, at least in a legal sense, that is an option. Without doubt, Congress has the authority to rescind the authorization to use force, without having to deal with the other side in the conflict. That’s why a proposal like the Reed-Levin proposal, which seeks not to place limits on achieving an objective, but to change the objective, has never been controversial on Constitutional grounds
7. But while the authorization to use force against Iraq remains in effect, Congress is on shaky ground, both legally and morally, trying to make tactical decisions about how to prosecute it. Congress’ power to declare war and to regulate land and naval forces was not intended to allow Congress to send troops into combat, then deny them certain options, even if conditions change. For the reasons outlined in point 2, the Constitution specifically places decisions about prosecuting a war outside the reach of Congress, and in the hands of a Commander-in-Chief in the executive branch who can (and is expected to) react more quickly.
Within our American Constitutional system, the legal and moral course for anti-war Democrats in Congress to pursue is ending the war, i.e. rescinding the authorization to use force against Iraq, and not to pursue measures that allow the war continue but might make it unwinnable.