We can't forget Hagel's comments when the insurgency peters out and Iraqis take over responsibility for their security.
That's a pretty meaningless statement on the part of Rumsfeld -- he can't hide behind the decisions of generals who he himself put in charge of this operation. Back in late 2002 and early 2003 there was a serious disagreement among military brass about the preparations for the war effort and the personnel levels that would be needed to maintain order in Iraq. The generals who supported the civilian leadership on this won out, so it's rather disingenuous for Rumsfeld to use "the generals" in his defense of the military effort in Iraq.