I'm quite sure this will happen. You only have to start thinking through how the withdrawal is likely to go. Iraq's government is a very uneasy coalition of people who are likely to get tortured and shot by fellow citizens as collaborators the moment the US leaves, and people who are effectively Iranian agents with heavily armed militias that in some cases used to be actual formations of the Pasdaran (Iranian Revolutionary Guards)
On the sidelines you've got the Sadr movement, again heavily armed, who are certainly going to be keen to create the appearance of having driven the US out the moment that it's opportune to do so and who will then want to take power, at gunpoint if necessary. Plus you have a whole bunch of mostly Sunni tribal groups who are also heavily armed, and don't really have any real stake in the largely Shia Quisling government, who the US has been buying off since the surge with local autonomy, big bags of money and lots of shiny new weapons (nominally so they can shoot 'Al Quaeda' on the US's behalf).
What the US has done since the 'surge' is achieved a temporary convergence of interests between a bunch of people who know they can't take on the US military in any serious way and not die, but would certainly fancy their chances against each other if the US military weren't around to interfere and hate each others guts. This isn't even a remotely stable situation if the occupation ever actually does pack its bags and bugger off back to Potatohoe.