Making that ultimatum to a country being bombed by the US is silly and unreasonable. Only if there is an evidence of Saddam being involved in those attacks, a retaliation would be justified, WITH OR WITHOUT any cooperation. Saddam can be relied on to continue to defy America, and neocons know it.
Buchanan is pointing out un-American interests in the neocon position and you are free to point out why a total war in Middle East is in the American interests.
I don't see any evidence of Buchanan adjusting his views to be just the opposite to the neocons', like you suggest may be true. What I see is a consistent position in both camps. The neocons' warmongering was predicted to happen right after the bombing. The motive is an important part of any analysis.
What Buchanan doesn't seem to grasp is that this war is not about him or the neocons.