[Note: I started this yesterday and should have posted it with the movies/war post--would have better explained my meaning.]
What the discussion over the Downing Street Memos lacks (see Crooked Timber, Dan Drezner, Kevin Drum) is the climate of opinion in summer 2002. This is how I remember it, without doing any research in old papers.
Remember that the history of Afghanistan was up and down, just enough to be suspenseful. Bush gave the Taliban a time limit to get rid of bin Laden, it expired, we saw some military moves, there was some speculation on the left and in the media about how the Northern Alliance and we were bogged down, then all of a sudden the air campaign took effect, the Taliban collapsed and everything seemed rosy. Speaking for myself, I exhaled a big sigh of relief. I don't remember significant opposition to the war, there were just enough problems for us all to feel relieved and joyous when Kabul fell.
What lessons did we draw from Afghanistan? Perhaps the same sort of lessons we learned when Netscape had its IPO--irrational exuberance. Particularly in the Pentagon--we had a new way of war, precision munitions, low casualties, and devastating effectiveness. So Bush, Cheney, and Rumsfeld justifiably felt their judgment was vindicated, their arms powerful. Liberals like me, who had been ready to leap on Bush for miring us in another Vietnam in Afghanistan, lost confidence. There was a new conventional wisdom abroad.
In sum, the Afghanistan war was an exception to Harshaw's Rule no. 1, you always fail the first time. But maybe I can get a reprieve for my rule, by adding a corollary: "but if you do succeed the first time, you'll get a big head." Witness the Blair Witch Project. Perfectly amazing success. But what was the name of the sequel? Very often in the history of movies the sequel is much inferior to the initial success (the Bridget Jones and Ocean's 11 sequels are examples).
Anyhow, in this theory Bush and Rumsfeld, enthused by their Afghanistan hit (pun intended), decided for a sequel in Iraq. I think it's true, as most of the bloggers on the Downing Street papers say, that they believed that Iraq had some WMD and wanted WMD and was bad and should be taken down. I also think they screwed the planning because of the euphoria from Afghanistan. They thought it'd be easy because Afghanistan had been easy. I'd also blame us liberals--I don't remember any vigorous opposition. There was a sneaking suspicion that Bush might be right, at the very least the country mostly was behind him. The most Congressional Democrats could do was to push for going to the UN. But that was just a slower road to the same destination. (No one ever came up with an alternative to war that seemed reasonable--doing nothing rarely seems reasonable.)
As E.J. Dionne said in yesterday's Post the administration fooled themselves. (Just as the producers of the Blair Witch sequel fooled themselves.)