Congress should and can stand up to Bush. From January:

[ProSense]

Yes, of course Bush might veto such a bill. And perhaps such a veto could not be overriden (although I would not be too sure about that). But even in that case, the lines of responsibility between the President and the Congress will be drawn even more starkly and clearly -- which would, I think, only be worthwhile, both for the Democrats themselves and for the Nation.

(UPDATE: The New York Times writes that "(i)n theory, could cut off financing, the only way it could actually interfere with the commander in chief’s plans. But Democrats have said they would not take such a step, largely out of fear of being accused of undercutting the troops. . . . That leaves them with only one option: holding a series of hearings, which start next week, immediately after the president’s speech, that are intended to expose the divisions within the military over the wisdom of increasing troops."

This is simply wrong. Congress does not have to "cut off financing" for troops on the ground. It could instead simply pass an appropriations rider providing that no funds may be used to increase the number of troops in Iraq (or specifying the extent to which such funds could be used for a troop increase, and conditions on such an increase -- examples of such legislation can be found on the final page of this Center for American Progress Report). Or the legislature could forego the appropriations route entirely, and simply pass a law prohibiting more than X troops in Iraq, and requiring whatever sort of "phased redeployment" the Democrats have in mind.)

If Congress does nothing to instantiate its strongly stated views about this most important matter of public policy, but resorts to mere pleading to the President to do the right thing, I fear that the Democratic Leadership letter will be viewed as implying that this is a decision for the President alone to make, and that Congress has no legal say in the matter. Nothing could be further from the truth.

link

The action should be in Congress, getting more Senators on board, not conceding to Bush's veto threat. They already passed a deadline, albeit without a veto proof majority. It's the Democrats that are backing down.