Iraq is the fruit of the poisonous tree

There is a legal principle called "fruit of the poisonous tree" by which evidence is inadmissable if it was generated from an unconstitutional or illegal act.  
In discussions about the Iraq War, I think we need to talk more about its poisonous tree --  the first mistake which is the mother of all the other mistakes made in this awful war.
The poisonous tree is the Bush Doctrine.