Kevin Drum makes a great point here regarding the pre-war intelligence problems in Iraq: they had become irrelevant by the time Bush launched the invasion. Once the UN weapons inspectors went in, the faulty intelligence became a moot point because we could verify it directly:
The fact is that by March 2003 we didn’t have to rely on CIA estimates or on the estimates of any other intelligence agency. We had been on the ground in Iraq for months and there was nothing there. There was nothing there and we knew it.
Did the CIA screw up? Probably. Did it matter? No. George Bush invaded Iraq in March 2003 not because he was convinced Iraq had WMD, but because he was becoming scared that Iraq didn’t have WMD and that further inspections would prove it beyond any doubt. Facts on the ground have never been allowed to interfere with George Bush’s worldview, and he wasn’t about to take the chance that they might interfere with his war.
I’m not sure that Bush knew the weapons weren’t there, but it’s pretty clear that he didn’t care whether they were or not. If he did, he would have invested a lot more into the UN inspections, rather than treating them as a distraction.