Its really rather simple
Bush/Cheney/Rumsfeld/Powell/Rice all claimed that there were hundreds of tons of weapons of mass destruction in Iraq. They all claimed that there were "ties" to Al Qaeda and spoke of 9/11 in the same breath. Both of these claims have proven untrue.
Your efforts to make this more complicated than that reveal a common desperation among the neocons who supported the war, grasping for any straw whatsoever to retain a justification for this despicable little war.
Its simple really...881 American soldiers have died in Iraq in pursuit of weapons of mass destruction that did not exist. It was Mr. Bush's administration that led the charge. He alone is responsible.