What do we really know about Al Qaeda? If we leave Iraq, and we can't really stay at this point, will Al Qaeda set up a new home to plot terror attacks against the U.S.?
Al Qaeda, to the extent we know much, seems focused on killing Americans. Living and working in the Washington, DC area, the thought of a terrorist attack is something to think about, because this is a likely target, should Al Qaeda or any other group with a similar bent get their hands on a serious means of mass killing.
But would a U.S. pull-out from Iraq really create a new nation state for Al Qaeda? This is an organization that has put it's brand on the killing of more Iraqi Shia civilians than U.S. soldiers. The Iraqi Shia will not be powerless when we leave, and nor will Iran, a Shia state.
How popular would Al Qaeda be with the Sunni neighbor states, like Saudi Arabia? Not very, under the current regimes. (regimes that are destabilized by the occupation).
How popular would Al Qaeda be with whatever new Sunni leadership in an Iraq that emerges from the current civil war? I don't think it would be that popular. Al Qaeda is a group of extremists who are bent upon a highly destructive conflict that if carried out against the U.S. will lead to retaliating and vast suffering for the hosts.
I don't think Al Qaeda is the future of Iraq. The U.S. occupation of Iraq has given Al Qaeda whatever popularity it has in the Islamic world. Our belated departure from Iraq will allow the Iraqi people to deal with Al Qaeda, and they are likely to be far more effective at curtailing its activities in Iraq than has the occupation by our highly vulnerable and greatly resented armed forces.