The only way additional troops could help...
Is if they have a specific targeted mission, such as wrecking the Madhi militias and blowing Sadr's ass away like a leaf. A number of others have pointed this out, too.
Somehow, although they certainly wouldn't telegraph such a mission, I doubt this is the case. I guess we'll see.
Incidentally, Bush is making a big mistake by putting an Admiral in charge of CENTCOM over the heads of Marine and Army choices.