With Iraq falling to pieces you can expect a lot of revisionist history coming so that it won't seem that President Obama carries a large share of the blame. Don't fall for it. Instapundit has everything you need here, including:
What Democrats were saying about Iraq before the 2003 invation
Administration bragging about how peaceful Iraq was (under Obama's watch)
Obama saying that preventing genocide would not be a reason to keep US troops in Iraq
An Obama tweet bragging that Obama kept his promise to bring US troops home, and mocking Mitt Romney for calling the decision "tragic"