So, Senator John Warner believes that Rumsfeld should stay, because we're "fighting two wars" right now, and that's an awkward time for a transition in leadership.

Indeed. That might result in haphazard decision making, based on a poor grasp of the facts on the ground or none at all, tactics which are insensitive to the sore points of the local populace, inflaming the situation, and inconstancy in overall strategy, alienating important potential allies within and outside Iraq. Better by far to stick with what we have right now.

Besides, as Matthew Yglesias points out, for a real clean sweep you'd have to ditch not just Rumsfeld, but his whole team, leaving a lot of unhappy former officials around to dish dirt. So even if Dubya were convinced, somehow, that this was the right thing for the country, he'd have to put that above his own electoral prospects. It'll never happen...