> Democrats and Republicans alike pushed for it based on the intelligence available at the time
No, they didn't; there was a bipartisan (but more Republican than Democratic) group that supported a hard line with war as the ultimate resort based on the unclear intelligence being put forward by the Administration, but the Administration (and, even before it existed as such, the element of the neoconservative movement from which it's foreign policy and defense leadership was largely drawn) was actively pushing for war for much longer, and deliberately engineered the intelligence (which was not merely spun, but actually falsified) presented to others, including in Congress, to build support for the war.
> To call him partially responsible for 100,000s of deaths is very unfair
It's entirely accurate, just as it is for the bipartisan group that supported the war in Congress, even though the administration did lie to them to build that support, since the information about the pre-existing intent of the Administration was readily and publicly available, and the debunkings of enough of the intelligence to make clear the administration’s absence of good faith was likewise available.