Anyone with an IQ above room temperature recognized that "Mission Accomplished" refered to the defeat of the Iraqi Army on the battlefield and the removal of Sadam from power and that it was kudos to the military for that. It obviously didn't mean that Iraq was instantly a democracy and all was well in The Merry Old Land Of Oz. Of course, no one ever accused the Dims of having the intellect or the honesty to realize that.
The banner was put up by the crew of the Lincoln. Their "mission" was accomplished.