Okay, the United States has officially withdrawn the last of its armed forces from Iraq as of today — but what have we left behind? Is Iraq in any better shape now than it was in 2005, when we might have pegged a troop withdrawal to the election of the Iraqi parliament? I don't think so.
US troops had been there roughly half a year when it was concluded that the "weapons of mass destruction" the Bush administration offered as a justification for invasion did not exist. After another couple of months, Saddam Hussein was captured and turned over to the Iraqis. We could have been gone by a year later, when they (very picturesquely) hanged him. They really didn't need us for that.
Today, Iraq continues to be splintered along religious and ethnic lines. Nuri Kamal al-Maliki shows little regard for the rule of law, the Iraqiya coalition of secular and Sunni Iraqis is boycotting the parliament in protest, and militias loyal to individuals like Muqtada al-Sadr have not been disarmed nor disbanded. No agreement has been reached with the Kurds about sharing oil revenues, and the Kurds seem willing to fight to maintain their autonomy. The forces of our allies in the "Sunni Awakening" are complaining of persecution by the majority Shi'a government. Iran's influence is extensive, and growing.
When the US leaves Afghanistan — at some unspecified date in the future — that country is likely to be even more disordered, corrupt, and crazy than Iraq is today. So, why wait? Let's bring all the troops home.