The Bush=Hitler line of argument is one of the most paranoid, and moderate liberals and leftists tend to avoid it because it makes them vulnerable to being painted with an extremist brush. When George Soros says that America needs a "de-Nazification" program, he is giving a generous gift to Bush-supporters. Indeed, the charge itself sounds fascist, since it appears to call for an overthrow of our democratic order.
And yet I see two parallels. First is the blitzkrieg. Like Hitler, Bush tried to run a war fast and on the cheap, and for the same reason: he didn't think there was public support for a heavier troop commitment to what was probably a war of choice. Second is that the war was started on a pretext. Hitler faked a Polish attack on Germany; Colin Powell presented "proof" to the United Nations that Iraq had WMDs. Of course, it's almost certain that the administration, and indeed even many war critics, believed that Iraq had WMDs. Even so, that may not have been the reasl reason for war.
But there are two big differences between Bush and Hitler. One has to do with means, the other with ends.
With respect to means, Hitlerian Germany did not respect any sort of rules of civilized war, but murdered civilians, not only without scruple, but as deliberate policy. The Jews were the most obvious victims of deliberate extermination-- Hitler even sacrificed the military effort to the implementation of the Holocaust, using trains that could have carried to troops and supplies to bring Jews to concentration camps instead-- but Hitler also conducted a war of extermination against the Slavic peoples of the east, where he wanted to use their Lebensraum for a fantasy empire. The Americans and their allies, by contrast, have conducted their war in a civilized fashion, with some famous lapses such as Abu Ghraib, but even these-- which do not come close to the ordinary practice of the Nazis-- have been punished and apologized for.
The great difference in ends is that while Hitler fought for overlordship, Bush's war was for liberation, without scare quotes. Hitler sought to bring the lands he invaded under German overlordship or directly annex them, but the Americans never dreamed of annexing Iraq, nor do they want to be informal overlords or indirect rulers; our desire to make Iraq democratic is perfectly sincere, and most Iraqis know that to one extent or another.
It's an interesting thought-experiment to think what would have happened, and what would have been history's verdict on Hitler, if he had conducted his invasion of Soviet Russia as a war of liberation instead of a war of conquest and extermination in pursuit of Lebensraum. Some Russians joined Hitler, wanting to fight against Stalin. (Sadly, contemporary Russians are still under the influence of Soviet propaganda enough to think that these people fought only for money.) Hitler was a (National) Socialist, and to spread freedom would have been against his principles. But had Hitler treated the Russian civilians well, and promised not to annex territory but to give the Russians a free constitution instead-- as we did in Japan and Germany later-- more Russians would have supported him, and he might well have won the war.
Could Hitler still have redeemed himself in 1941? The Holocaust hadn't really begun at that time. Suppose Hitler had conducted the war against the Soviets as an international crusade of liberation against Bolshevism, pledging to give the Russians a free constitution, winning, and fulfilling his pledge in due course. Then sued for peace with Britain, which he always wanted, and got it (for what could the British do with the Soviets gone?). Europe would consist of: 1) a new post-Soviet rump of Russia, stripped of its various subject nationalities, governed perhaps by some restoration of something like czarism; 2) new states like Ukraine, the Baltic states, Caucasus states, perhaps an independent Chechnya, carved out of the Russian empire, all to some extent satellites of Germany; most of western Europe under German overlordship; and a Britain still free but a bit less proudly triumphant. Certainly Hitler had already done plenty of nasty things before that for which historians would blame him, but many might conclude that on balance his work had been for the better. Perhaps this course was impossible because of the nature of his personality and his regime; but then, it would have served Germany's national self-interest much better than the course that actually was followed.
I think Europeans and Americans agree in seeing Hitler as the ultimate evil, but for different reasons. For Americans the reasons are primarily liberal and humanitarian: all those people he tortured and killed, plus the totalitarian nature of his regime, the burning of books and all the other crimes against freedom. Europeans are soft on totalitarianism: Communist parties are mainstream there, not anathema as in the US. They tend, I think, to blame Hitler chiefly for being an aggressor, understandably since their countries were aggressed-against. So in the Iraq War, Americans thought Saddam-- the genocidal totalitarian-- was the analogue of Hitler, while some Europeans saw Bush and Hitler as fellow initiators of wars of choice.