I'm late coming to it, but I think Andrew is wrong about this:
I can still just about believe that Bush thought the WMD case was sound. I can't believe, given all that we now know, that Cheney did. He's too smart. The data he read, we now know, was far more equivocal than the data the public was provided with. He's not new at this. He probably never wanted to make the WMD argument anyway, put it in to appease the UN crowd, and certainly wasn't going to query its validity. We may never know, of course, because Cheney will have destroyed the evidence, but if I had to guess, I'd say it's obvious Cheney knew all along that the WMD line was a cover, not a real threat, but realized by the summer of 2003 that any hint of this leaking (even from a two-bit blowhard like Wilson) needed swift and brutal rebuttal. They were embarrassed enough by the WMD bust, but if it was revealed that they had ignored all the caveats beforehand, it could get really dicey.
Now I don't know Dick Cheney, obviously, and I don't claim any special knowledge of his motivations. But I do know some very smart (albeit junior) people inside the government who were looking at the same data Cheney was looking at in 2002 and 2003, and who drew exactly the same conclusion that his pre-invasion remarks suggest that he drew - namely, that Saddam's programs were probably more extensive, and more dangerous, than our intelligence suggested. That's the thing about equivocal evidence: People read it through the lens of their pre-existing biases, and the pre-Iraq War biases on the Right (and not only on the Right) were similar to the biases that led the Committee on the Present Danger to overestimate Soviet strength in the 1970s - specifically, a belief that dovish analysts elsewhere in the government were underestimating the capabilities of America's enemies. In both cases, highly intelligent people got things dramatically wrong, by reading into incomplete evidence and drawing unwarranted conclusions that dovetailed with their own political prejudices. In neither case, I think, do you need to assume duplicity to explain what happened. Cheney may have misled the public about how solid the intelligence was that led him to draw the conclusions he did - and I don't mean to defend such conduct - but I'm willing to bet that he believed those conclusions as strongly as Bush did, if not more strongly.
I would also note that the best explanation I've seen advanced for why Cheney circa 2001 was gung-ho for doing what Cheney circa 1992 thought was a bad idea - toppling Saddam and occupying Iraq - is the psychological impact of the mid-1990s revelations that pre-Gulf War Iraq was far closer to getting a nuclear weapon than anyone thought at the time. The fact that we had significantly underestimated Saddam's capacities in the past seems a more likely reason for Cheney's post-9/11 tendency to dramatically overestimate Saddam's capacities than the implausible motives Andrew imputes to the Veep: A willingness to agitate for an invasion on grounds he knew to be bogus, in the full knowledge that if the invasion came to pass he would be exposed as a liar.
Photo by Flickr user tswartz used under a Creative Commons license.