Now...
U.S. field officers said the Marine battalion spearheading the fight had suffered significant casualties in a battle with [link|http://define.ansme.com/words/i/irregular.html|irregular] guerrilla fighters known as Saddam's Fedayeen.These are NOT military units.
They are the citizens of Iraq who hate the US invasion so much that they are willing to fight on their own, without Saddam's control.
This is the "quagmire" that was predicted.