Really, it's all a matter of trust.

The simple truth is that Powell could have produced all the evidence in the world to show that Sadaam has WMD and it would have made very little difference because he chose also to present the flimsiest of cases for the Al Qaeda link at the same time as if the evidence for the latter was as strong as the evidence for the former. If they will lie, obfuscate, and deceive on this matter then how are we to trust them on anything else? Indeed, given the raw nerve that is 9/11, the fact that the Bush administration would use terrorism as an angle to sell a war against Iraq makes it even worse. It means that Bush is willing to traumatize people with memories of that awful day in order to get what he wants. That's not what I call a trustworthy leader.