The greatest failure of Rumsfield was after the 2004 election we could have boosted US troop levels, increased the size of the Army, and got rid of the Madhi Army and really cleaned out Western Iraq.
Instead he continued to believe this less is more idea of warfare which allowed Zarqawi to finally spark a major sectarian conflict in Iraq making stabilizing the country much harder and making the war much less popular in the US.
Rumsfield should be removed as such general Abaizad who also believes in the Rumsfield docterine.
More troops would have meant more targets and more pissed off Iraqis and fewer would want to "stand up." I am no fan of Rumsfeld but he was right to oppose more troops. More troops would be like giving more money to a welfare recipient or pouring more federal money into a poor neighborhood in Chicago.