It's a nasty, no-win situation.
Stay, continue to inflame just about every yahoo with an Kalashnikov in the region, and draw in many from outside, prolonging bloodshed.
Stay, take responsibility for destruction and try to put things together.
Go, remove the only halfway professional force in the country, abandon Iraq to what looks like a well-nigh unsolvable bloody mess.
Go, remove the inflaming factor, reestablish the reputation of the US.
Who knows