Almost nobody in Congress actually wants to pull funding as the mechanism for bringing the troops home. The vast majority of Democrats, and the Republicans who would be willing to cross the line, want to incorporate some sort of deadline or schedule into the funding bill.
The problem is the veto threat, and if Bush knows that by vetoing the bill he can get a new one without any deadlines, there is absolutely no pressure on him to sign it.
I don't think it's likely that this is going to work. Even if the Democratic leadership really cracked the whip, Bush is completely stubborn on Iraq and he has the benefit of unity. It's almost impossible to get a few hundred legislators to be as unified and resolute on an issue as a single president, especially on one that a lot would consider politically dangerous.
But just because it's probably going to fail does not mean they should not even try, and if they're going to make a real attempt, there has to be a somewhat credible threat that this is the only version of the bill that's going to come across his desk.
It's bad that this has to happen in a way where people might feel the troops are being hung out to dry, but it's about the only thing Congress can do. They could try to revoke the Authorization for the Use of Military Force, but that wouldn't stop it. The Gulf of Tonkin resolution was revoked and Nixon kept the troops in Vietnam (he actually encouraged that vote so he could assert the executive's authority).
