Interesting take on the Lancet figures from Marginal Revolution:
A very high deaths total, taken alone, suggests (but does not prove) that the Iraqis were ready to start killing each other in great numbers the minute Saddam went away. The stronger that propensity, the less contingent it was upon the U.S. invasion, and the more likely it would have happened anyway, sooner or later. In that scenario the war greatly accelerated deaths. But short of giving Iraq an eternal dictator, that genie was already in the bottle.
If the deaths are low at first but rising over time, it is more likely that a peaceful transition might have been possible, either through better postwar planning or by leaving Saddam in power and letting Iraqi events take some other course. That could make Bush policies look worse, not better. Tim Lambert, in one post, hints that the rate of change of deaths is an important variable but he does not develop this idea.