It's worth noting that impeding the march to war was the exact point of the constitutional clause mandating that both chambers of Congress be given the responsibility for declaring war, as the debate during the Constitutional Convention makes clear. When the royalist Pierce Butler of South Carolina formally proposed giving the president the power to start war, Elbridge Gerry (the man for whom "gerrymandering" is named) of Massachusetts said that he "never expected to hear in a republic a motion to empower the executive to declare war." Butler's motion was quickly rejected. Explained Virginia's George Mason, the president "is not safely to be entrusted with" the power to decide on war. Mason therefore favored "clogging rather than facilitating war."
Presidents have long ignored the War Powers Act, and Congress has studiously done nothing about it. As for declaring war, forget it. The United States hasn't formally declared war on another country since the end of World War II.
If liberals wanted to team up with originalist conservatives on something, I think changing this would be a worthwhile project. It's certainly the case that the president needs to have the authority to respond quickly to events, and it's equally the case that Congress doesn't want to get involved in every minor use of American troops abroad.
But there ought to be a limit. In the case of a major foreign war involving detailed planning and serious numbers of troops, the president ought to be required to get a declaration of war from Congress. Defining "major war" isn't a trivial task, but it's not impossible either. Since 1990, the United States has been involved in at least four major wars--the Gulf War, Kosovo, Afghanistan, and Iraq--which should have required a declaration of war. None of them got it.
Moreover, the Contitution requires that Congress declare war is not just to limit the possibility of tyrannical rule, but also to guarantee that the political establishment get political "buy-in" before it wages war. The goal is to ensure that the people themselves are committed to the process themselves, so that they will stay steadfast in a long struggle. This need to establish popular commitment to the cause of a war is why the Constitution mandates that it be not just the Senate, the main organ of "advise and consent" to the President in matters of foreign policy (as in the approval of treaties and ambassadors, for example), but also the House of Representatives, the people's direct representatives, that approve a declaration of war. After all, if the President de facto declares war unilaterally, it's not surprising if national commitment to war slowly bleeds away as the going gets tough. But basic psychology makes it evident that steadfastness in the face of trouble is much more likely when the people's proxies have directly committed to war. This is why Kevin is exactly right to conclude:
Ultimately, this is a nonpartisan point: these clauses in the Constitution exist precisely to ensure that the Commander-in-Chief, who has the exclusive responsibility for how a war is waged, cannot enter a war to which the people themselves are not fully committed. In short, it exists as a safeguard both against tyrrany, and against the possibility that our country can function as an empire.
One of the great travesties of the Iraq war is that Congress passed a "use of force" resolution in October 2002 and then passed the buck to the president to decide if and when its conditions for war had been met. Five months later we invaded Iraq without Congress doing anything further aside from approving some budgetary items. This allowed many members of Congress — mostly Democrats — to argue disingenuously that, sure, they approved the October resolution, but they didn't approve of the war as George Bush prosecuted it. They felt the conditions of the resolution hadn't been satisfied.
Frankly, they shouldn't be allowed to get away with this. It's one thing to pass a use of force resolution or to approve funding for a troop buildup. But when it comes time to pull the trigger and go to war, Congress should explicitly approve it without conditions. Based on its own evaluation of current facts on the ground, Congress should either approve military action at that point in time or not. This puts our elected representatives on the record about the act itself, and that's as it should be. It's long past time for Congress to stop ducking its constitutional responsibility.
With all that said, I must say that it's obviously absurd to think that this could actually be a cause for finding common ground with the constitional "originalists" like Scalia etc. To think that this crowd is the least bit consistent about their commitment to a literal reading of the Constititon, is a joke -- and one in poor taste, I might add. These guys are merely apologists for fundamentalist moralizing and unimpeded corporate power, who merely intellectualize their hackery by referring in the most selective possible way to the "original intent" of the founders.