They should use Congress as their bully pulpit -- to pass a resolution expressing their lack of confidence in Bush's new plan, to subject his new Iraq team to tough questioning when it comes to testify, and, above all, to hold the Bush administration accountable for achieving the progress he promised Wednesday. (Accountability could come in the form of more hearings and resolutions, as well as investigations.) Democrats could also usefully press the White House to start planning for the worst -- large scale ethnic cleansing, refugee flows, and regional intervention -- should Iraq spiral deeper into chaos.

Some Democrats would like to go further -- by withholding funding for the additional troops. For a variety of reasons, however, this is a bridge too far. First, where Democrats (joined by some Republicans) would unite behind a resolution disapproving the Bush plan, many will be loath to cut off funding for troops that have already started deploying to Iraq. Why put the party's disunity on public display?

Third, while Congress absolutely has the constitutional power to withhold funding, it's the political equivalent of going nuclear and should be used sparingly. Without giving Bush a blank check, Congress can serve notice that it will periodically measure the expanded force's progress against the president's promises. Moreover, a cut-off now would likely be a demoralizing blow to the 132,000 U.S. troops who are already risking life and limb in Iraq.

Fourth, a congressional effort to cut funding would be seen in the country as an attempt to seize control of Iraq policy. If there is to be a calamitous, Vietnam-style U.S. defeat in Iraq, Karl Rove would probably like nothing better than to goad Democrats into assuming co-responsibility for it. There's no reason to fall into this trap now. So Democrats should speak their minds, hope for the best in Iraq, and be prepared to hold the president accountable if his latest plan fails.