Buried at the end of this LAT article on Iraqi PM Nouri Maliki and the decline of American influence in Iraq is this passage:
At the same time, Iraqi officials complain about the United States’ failure to create a lasting foundation beyond its military presence. Iran has created more than $2 billion in trade with its neighbor, including fuel and electricity exports.
This, in a nutshell, explains why we might eventually wind up leaving Iraq with a military draw and a strategic defeat. It also, for that matter, explains why we might eventually set aside our ideological differences with Iran and strike a grand bargain: we’re both trading nations at heart.