The call for de-authorization has some support from, for example, Senator Barack Obama and Governor Bill Richardson (NM). However, it also has run in to opposition from other high-profile war opponents, such as ex-Senator and presidential candidate John Edwards.
Senator Clinton hopes that de-authorization would remove the legal authority of the president to continue the war and force Bush to ask Congress for new authorization. But, would a Act of Congress rescinding the AUMF have that effect? As the New York Times puts it:
The Times is right that passage of a de-authorization bill (although it would certainly be vetoed, just as the appropriations bill was) might very well provoke a critical constitutional debate over the nature of war powers, but I think they've got the grounds of that debate wrong. The president would most likely claim that he does not in fact require congressional authorization to conduct military operations, and that requesting such authorization is not a legal necessity but rather a political nicety.
Even if Mrs. Clinton and Mr. Byrd succeed in their effort, it is not clear whether President Bush would have to withdraw troops, or if he could resist by claiming that Congress cannot withdraw its earlier authorization but instead has to deny money for the war to achieve that result.
The question could prompt a constitutional debate over war powers that only the federal courts could resolve.
One argument that I have made several times is that the continued funding of a standing army, in light of congressional awareness of how that military has been used in the past, constitutes a de facto congressional authorization of military operations. Thus, just as every president since Nixon has rejected the War Powers Resolution, in this view, Congress does not have the power to oversee and control (short of cutting off funding for the troops) each and every use of military force. The congressional power to declare war is, according to this argument, more about the president's ability to take legislative action pursuant to the conduct of the war than it is about giving Congress authority over the deployment of force.
As I have noted before, no one really knows how the judiciary would decide. Which is why a Supreme Court hearing on this would be welcomed. However, it's not likely to happen. Congress is unlikely to muster the political will to pass de-authorization legislation (in my last post on these issues, I noted that the puzzling language in the appropriations bill suggested a need to soften the language of the bill to attract enough support for passage). And even if Congress manages to pass such a bill, if it couldn't override the veto of the appropriations bill it doesn't seem likely to override a veto of what is sure to be an even more controversial bill. So while we might like to see a showdown over this, I wouldn't keep your fingers crossed.