Rumsfeld was the architect of the military strategy that resulted in the Iraqi civil war, and was one of a few very loud voices in the administration in the aftermath of 9/11 militating for an invasion in the first place.
You're arguing that Rumsfeld was incompetent? I'd say he's among the most competent executives ever to deliver to his superiors exactly what they wanted.
Without hindsight bias, and considering that selling a cheap war was critical to getting buy-in from congress, Rumsfeld architected a great plan.
I'd argue that Rumsfeld is an incredible intellect and expert tactician who made zero mistakes.
