The problem with that premise, at least in my less than humble opinion, is that it ignores the inevitable political repercussions. Political acts always have a cost in political capital. Simply defunding the war would have an enormous political cost that would be paid in 2008 and beyond. The political ramifications of withdrawing funding are very real and play directly into Republican hands. Defunding the Vietnam War lost Democrats a sizable slice of the electorate, the military voter, for 30 years. In the 2006, Democrats have made some real inroads into that group and surrendering it at this point does not make sense when there are a few other moves that can be made. To argue against such an act, I felt it was important to come up with what I think should be done. The following list is what I think should be done, not by the Democrats, but by our Congress:
Pass a resolution demanding that Bush withdraw American troops. It would have to be non-binding because such a demand would never pass a constitutional test, as I understand it. It expresses Congressional disapproval based on the political demands of a majority of Americans.
Pass a binding resolution demanding that no more troops be sent without authorization by Congress under the War Powers act. This is also on shaky ground, constitutionally. It should be done first and would likely pass a constitutional test. They are not saying no, merely informing the President that only Congress has the power to make war.
Refuse to pass war funding as emergency authorization. If President Bush wants to fight the war, he has to do it within the normal budgetary process.
Formally make it Congressional policy that any war funding must be paid for by new taxes. Take 100 billion a year to fight a war, remove 100 billion a year from tax breaks for the rich and Corporations. Take the money from those who benefited primarily from the tax cuts and they will lose their ardor for the war. This spreads the sacrifice around.
Formally investigate all contracts with civilian companies for services during the war and mandate that only the lowest bidder from a pool of secret bids will be accepted. This policy attacks the profits made by such companies as Halliburton and will cool their ardor for the war.
Withdraw the authorization to use force. Saddam is gone. We have successfully performed regime change. Congressional investigation has found that there was no link to Al Qaeda, and the government linked to Al Qaeda no longer exists, anyway. The same argument can be made for WMD's; they no longer exist, if they ever did. With Congressional approval to use force gone, it forces President Bush seek authorization to use force in the current Civil War. The American people are loath to do this.
Initiate a formal investigation into the sources of intelligence to find out why it was so wrong. It is obvious that 9/11 and the war in Iraq were caused by massive Intelligence failures. Without fixing the problem, we will suffer their failure again. Of course, if the Intelligence was cherry picked, this could cause real problems for the current administration.
Launch formal investigation of all signing statements and take any refusal by President Bush to follow the law to the Supreme Court and make him defend it. The Unitary Executive Privilege he has claimed is not mentioned in the Constitution that I have read and seems to violate a number of specifically named powers. This action forces the current administration to drastically alter its actions.
Investigate the rumors that President Bush has authorized a secret war on Iran and Syria. Subpoena the President and ask him direct questions. Subpoena any classified memos discussing Iran and Syria. This action sparks a direct confrontation with the Whitehouse, and will be argued with at least one trip to the Supreme Court. Since only Congress can authorize war, they are within their power to investigate such a rumor. If they find evidence that the Executive has authorized a clandestine war with Iraq with no authorization form Congress, he has directly violated his powers under the constitution.
If the above items fail, then use very specific line items for each piece of military spending, in order to refuse funding for the escalation. This will not work, because the executive has enormous leeway to shift spending within the defense budget, but they can try, but it will haunt them and possibly lead to the loss of Congress and the Senate.
Defunding Iraq is an action that will have drastic consequences with independents and centrist Republicans that voted with Democrats in 2006. It will absolutely loose the military voters, who are now coming back to the Democratic Party in a big way. Soldiers serving in war zones will see defunding Iraq as a direct attack on their lives. They did not ask to go there. Defunding Iraq will be the center of the Republican marketing plan, and will work on at least 10% of the electorate. In our polarized society, 10% will swing the majority. It all comes down to which party Americans see as best serving their interests.