Due to the nature of the exit, I place most of the blame on Bush for invading Iraq in the first place. It has arguably been the worst error in US foreign policy for our interests since Vietnam.
on the contrary.
tho i do not support us interventionism , in a militaristic scale, especially in the middle east, i can objectively observe that Bush had implemented necessary and key military policies that broke the camel's back in regards to insurgent resistance in iraq eg, the surge that was designed by gen. david petraeus. in fact when bush left office, the united states and the iraqi military had greater command and control of iraq , beaten back the forces of al sadr, and also squashed takfiri insurgents near tikrit. the issue arose when obama, who ran on the platform of removing us forces and decreasing us-iraq defense partnerships, implemented that policy, which he had promised. he also implemented a timeline , which the insurgents took into consideration and thus hid and lay in wait. until the americans moved out. with us encouragement of a majority shia led government and inhibiting sunni population, this led to the genesis of seprationism, coupled with the civil war in syria, the porous border between syria and iraq and the recent military training cia operatives gave to moderate syrian rebels --- well, iraq was simply fertile ground, so to say. it was a powder keg bound to happen absence of a military command structure.
the problem was the american forces left too quickly, not considering the ill effects of a vacuum.
regards,