Along with Brookings scholar Philip Gordon, O'Hanlon wrote in the "Washington Post" in late 2001 that any invasion of Iraq would be difficult and demanding and require large numbers of troops. This article led to Kenneth Adelman's famous prediction of a 'cakewalk' in a subsequent rebuttal in that same newspaper, but Gordon and O'Hanlon's argument was validated by subsequent events on the ground. He argued at a major forum on Iraq at the American Enterprise Institute (AEI) in the fall of 2002 that an invasion of Iraq could lead to 150,000 U.S. troops remaining in that country for 5 years, while expressing his view that a war should occur only if inspections failed to fully confirm the disarmament of Saddam's stocks of weapons of mass destruction.