Imagine the following scenario:
March 17 (or whatever deadline is [or is not] approved as the start of war) rolls around. Dubya announces that Iraq must be disarmed by military means, and gives the green light for a military invasion of Iraq by US forces. A thousand journalists are on-hand, videotaping every event leading up to the cruise missiles launching and bombers taking off. Several battalions stand ready to begin the ground invasion.
Suddenly, on live TV, to the horror of Dubya watching, US soldiers en masse lay down their arms and begin protesting the invasion. Pilots emerge from their bombers refusing to fly missions, and Navy enlisted men refuse to press the button(s) that initiate cruise missile launches. It turns out that a vast secret petition has been circulated among all US non-commissioned forces (in other words, the grunts) stationed in the Gulf. Any soldier who signed the petition would refuse to carry out the orders to invade Iraq, despite the possible ramifications, such as being thrown in prison, being branded a deserter in wartime, etc.
What would happen? I would think that if anything like this happened, even on a small scale (say, only a few thousand soldiers in real life), it would already be a huge psychological victory for Iraq. Could the US conceivably still go ahead with the invasion, even if it meant that some vital services (radar, refueling, etc.) would not be performed?