Surely John Derbyshire isn' this sheltered. "While my scorn for the 'Bush lied, men died' gang is every bit as great as yours, it is a fact that no American, in March 2003, thought we would have a huge army planted in Iraq 2½ years later."
Obviously Bush, Cheney and Rumsfeld had no clue about what would happen. I think most neocons figured that the Bush Victory tour would have moved to Syria and Iran by know. But looking at the premier issue of The American Conservative, from October of 2002 I found an article by Eric Margolis called Iraq Folly which spoke of a coming "quagmire" and said, "Though U.S. forces could quickly defeat Iraq’s regular army in the field, there is a high risk of prolonged urban guerilla warfare and great numbers of civilian casualties." The same issue had a Pat Buchanan column that I have quoted many times. "With our MacArthur Regency in Baghdad, Pax Americana will reach apogee. But then the tide recedes, for the one endeavor at which Islamic peoples excel is expelling imperial powers by terror and guerrilla war."
I could find more examples of people warning of the consequences of invading in 2002 and early 2003, but when it would have helped, they were drowned out by the cakewalk brigade.