No debate here in undisclosed location, though if I were a dedicated blogger I'd read through transcript part the first which just arrived in my inbox. But my problem with the "residual forces" idea is that it just seems to be one of these "split the baby" ideas to demonstrate seriousness and fealty to bipartisan compromise. It doesn't actually appear to have any genuine strategic rationale, it puts the lives of troops at risk, it maintains genuine perception of the US as an occupying force welcomed by a puppet government, etc.
I have yet to see a rationale for such a thing other than "they should be there just in case."