I put this in a comment but decided to make it a diary.
I have come to rely on Harry G. Frankfurt's little book
On Bullshit (Princeton UP, 2005) to discuss the invasion and the rationale with Bush supporters. Frankfurt distinguishes between lies and bullshit as follows: the liar knows the truth, and tries to steer us away from it. The bullshitter doesn't care what the truth is. "Bullshit," says Frankfurt, "is a greater enemy of the truth than lies." From this perspective, it's not as though Bush et al.
knew there were no WMD in Iraq. Rather, they didn't
care whether there were or not: they just wanted in.
Consider the question:
Did the Bush administration lie to start the war?
Most people now will say yes. But a hard core of support won't move. However, reframe the question around bullshit, and make sure people understand what this means. If people understand the distinction between lies and bullshit, consider the question:
Did the Bush administration bullshit to start the war?
I think a much larger number will say yes.