What if before the 9/11 attacks, Iraq shoots down an American military or reconnaissance aircraft with a live crew before the September 11 attacks in 2001 during the presidency of George W. Bush?
Iraq shot down a U.S. drone on 911 itself and it meant nothing. I doubt anything would change even if it was manned.
http://edition.cnn.com/2001/WORLD/meast/09/11/iraq.shootdown/
You have to understand Bush bought into the whole UNSC approved military action being the way it should be done notion and was convinced of it by Powell, Blair and his father's experience. But, Putin is not Gorby or Yeltsin. Putin actually spent over a year stringing Bush along after 911 that he might support toppling Saddam and this is a period most of which if Bush went in along there would have been little domestic or international outcry if he went it alone.
He let anger build into million man anti war marches in Western Europe and let the enemy have time to plan and organize which meant much much more problems and then went in. France bowed out under public pressure and the German government was going to go with whatever Putin decided.
Bush now would realized Putin was playing him and he was never going to get UNSC support, but didn't at the time.