Just my two cents, but by the time 2002 rolled around, I really believe that Diplomacy had gone as far as it could possibly go. Diplomacy has it's limits, and just my opinion, but in the case of Saddam, those limits had been exhausted.
But the whole situation is murky. To this day, we really don't know if the entire nation building of Iraq was a part of the plan or not. It's quite possible that once we got into the briar patch, we saw that the only way out was a complete re-do of the country. That we've done much of our work on the fly; I hate to think that's the case, but not everything in history has been meticulously planned.
There really are multiple phases to the Iraq argument, which is what makes it so interesting. Whether or not to remove Saddam, if we remove him, how to remove him, etc.; it's really quite fascinating.