We had an intervening event between W's election and the invasion of Iraq -- 9/11. That changed the geopolitical calculus. It's a poor President indeed that cannot adapt his foreign policy to changing circumstances.
Good post. Interesting that even under Reagan there was a "realistic" approach to most foreign policy. It was the US approach and until Reagan set out to destabilize the USSR indirectly with the war in Afghanistan did we change a little. Panama and Granada were more in keeping with the Monroe Doctrine than a break with "realism".
However, as you point out, since 9/11 the US has shed the "realistic" policy in some parts of the world, but we are still in that mode in others. The State Department does not like hard work and a "realistic" Foreign Policy requires it only to keep the status quo while one that promotes the spread of democracy requires work, intelligence and perseverance, three things lacking in our State Department.