How do we compare mass murderers?
In a way, debating which was the worst of the totalitarians seems kind of obscene. In terms of innocent people killed, it appears that Mao or Stalin might have more blood on their hands than even Hitler. Pol Pot directed the autogenocide of 1-3 million people, making his one of the worst on a per-capita basis. Idi Amin was responsible for the deaths of several hundred thousand people, and Saddam not only started a war that killed over a million people, he's probably responsible for somewhere around 300,000 murders of Iraqis.
And compared to that admittedly incomplete list, what has Bush done that even remotely compares?