I think that Bush is quite possibly the worst president that the US has ever had.

Having said that, comparing him to Stalin IS quite a stretch. Stalin is one of the very worst dictators that the world has ever seen, and as Chromeboomerang notes below, was literally responsible for the deaths of tens of millions of people. Bush, in his own way, is doing even more damage than most people realize, but the sheer scale of evil really doesn't compare. Even if you, for example, believe that one millions Iraqis have died in the war (the number seems implausibly high to me, though it seems possible), and that the US is directly responsible for all of those deaths (pretty questionable, although we have certainly played a part), then Bush has a long way to go before he's even remotely in the same league as Stalin.