I worked in the intelligence business for about 30 years; 5 years with CIA (as a case officer in the Arab world); 25 years in Army Reserve Military Intelligence, involved with strategic analysis. So I do have a reasonably good idea of how the system works, how National Intelligence Estimates get written, etc.
The facts on Iraq are these: Saddam had (and used) chem weapons, both against the Kurds in his own country, and against Iran in the Iran-Iraq War. There is no dispute as to those facts. And no, we did NOT provide him with those chemical weapons. The "assistance" we gave Iraq during their war with Iran consisted largely of information based on satellite imagery, which was undoubtedly of great value to the outnumbered Iraqi military. But if you look at the equipment with which Saddam fought that war (and the Gulf War, and the 03 invasion), it is nearly all Russian. Not stuff we gave him.
In the intelligence business, when you know something for sure--as we knew that Saddam had chem weapons--you tend to cling to that knowledge with great tenacity, because there is a whole lot you don't know. And in the case of Iraq, after the Gulf War we simply did not have reliable assets in place, in country, to tell us what was going on. Therefore, when the UN inspectors left Iraq in 1997 and said there were hundreds of tons of chem weapons unaccounted for, there was absolutely no reason not to believe them. We did not have anyone telling us that Saddam had destroyed those stockpiles, given them away, or that the starship Enterprise had dropped by and beamed them up. And we did have a number of refugees--anti-Saddam types of course, who were not tested, reliable sources (but you go with what you've got)--telling us that yes indeed, those weapons were still there.
In my case, as a former intelligence officer--I retired with the rank of colonel, and was the first commander of the prototype Joint Reserve Intelligence Center, which was providing strategic analysis support to the US European Command--I often find it necessary to explain to the uninitiated how the whole process works. Many have criticized Tenet, saying he should have advised the president against invading Iraq. Wrong! The role of the Director of Central Intelligence (now taken over by the DNI) is that of chief intelligence ADVISER to the president. You cannot be both an intelligence adviser and a policy advocate. If you start advocating for a particular policy, then your objectivity as an intelligence adviser rapidly becomes suspect.
I'm not necessarily a Tenet supporter, and I thought his "slam dunk" explanation was particularly weak. However, he summed up the role of intelligence in relation to policy very accurately in his Feb 04 speech at Georgetown:
"The risks are always high. Success and perfect outcomes are never guaranteed. But there's one unassailable fact: We will always call it as we see it. Our professional ethic demands no less." Amen to that.
Interestingly enough, if you listen to any of the several former intelligence officers who have come out of the woodwork to criticize the Bush Administration and its decision to invade Iraq, you will not find a single one that makes a good case for the books having been cooked on WMD's. They'll talk about Cheney and Wolfowitz looking for links between Saddam and AQ, Saddam and 9/11--but the record also shows, quite clearly, that the CIA never caved to that pressure. They never stated that there was any substantial relationship between Saddam and AQ, and no connection at all between Saddam and 9/11. The fact that Colin Powell--no stranger to intelligence, given his military career--believed the WMD intelligence and made that now-infamous UN presentation is quite telling. As is the fact that the WMD assessment never really changed, from what the CIA told the Clinton Administration (and remember, Tenet was a Clinton appointee) and what they told the Bush Administration. It proved to be wrong, but I don't see any evidence that it was anything other than an honest (and quite understandable) mistake.
As for missing 9/11 . . . much of that had to do with internal problems within the intelligence community, caused to a great extent by legal interpretations which severely hindered information sharing between CIA and FBI, and even within FBI between counterintelligence/counterterrorism officers and law enforcement officers. We missed Pearl Harbor too, and if anyone were to examine the history behind both events, I think they would conclude--as I have--that we had a lot more to go on prior to Pearl Harbor than we did prior to 9/11.
