It's the Congress folks - what holds the purse strings....
Iraq is more of a Guerrilla war now, more troops would most likely get in the way.....rotation is for Peace Time - this is War Time - seasoned troops are what we need, not green soldiers. WWII saw soldiers in the theater for as long as four years....Only Andrew Sullivan and John Kerry think four months is enough time to spend fighting a war...........
Our troops were sent in to destroy Saddams military and capture his key operatives. That was extremely successful with our initial troop levels. More initial troops would have probably translated to more terrorist targets after achieving those primary goals. We are however getting close to the time for the slow withdrawal. Cannot be done however until a stable government is in place. I believe the troop level we have in Iraq now is the same troop level we initially sent onto the beaches of Normandy to free France from Germany. Now that initial WWII troop level turned out to be too low, but it was quickly increased. The Fascist Germans were much tougher foes.