Here is an important point about troop levels that some of Rumsfeld’s more simplistic critics miss–it’s not how many troops you have necessarily, but what kind of troops doing what. Tom Ricks has written a blisteringly critical account of the Iraq war, but his line on troops is not the simple conventional wisdom (not that having the wrong kind of troops doing the wrong thing is great either):

Exacerbating the effect of this decision were the U.S. Army’s interactions with the civilian population. Based on its experience in Bosnia and Kosovo, the Army thought it could prevail through “presence” — that is, soldiers demonstrating to Iraqis that they are in the area, mainly by patrolling.
“We’ve got that habit that carries over from the Balkans,” one Army general said. Back then, patrols were conducted so frequently that some officers called the mission there “DAB”-ing, for “driving around Bosnia.”
The U.S. military jargon for this was “boots on the ground,” or, more officially, the presence mission. There was no formal doctrinal basis for this in the Army manuals and training that prepare the military for its operations, but the notion crept into the vocabularies of senior officers.
For example, a briefing by the 1st Armored Division’s engineering brigade stated that one of its major missions would be “presence patrols.” And then-Maj. Gen. Ricardo S. Sanchez, then the commander of that division, ordered one of his brigade commanders to “flood your zone, get out there, and figure it out.” Sitting in a dusty command tent outside a palace in the Green Zone in May 2003, he added: “Your business is to ensure that the presence of the American soldier is felt, and it’s not just Americans zipping by.”
The flaw in this approach, Lt. Col. Christopher Holshek, a civil affairs officer, later noted, was that after Iraqi public opinion began to turn against the Americans and see them as occupiers, “then the presence of troops . . . becomes counterproductive.”
The U.S. mission in Iraq is made up overwhelmingly of regular combat units, rather than smaller, lower-profile Special Forces units. And in 2003, most conventional commanders did what they knew how to do: send out large numbers of troops and vehicles on conventional combat missions.
Few U.S. soldiers seemed to understand the centrality of Iraqi pride and the humiliation Iraqi men felt in being overseen by this Western army. Foot patrols in Baghdad were greeted during this time with solemn waves from old men and cheers from children, but with baleful stares from many young Iraqi men.