I think he won because of it, not in spite of it. That's speculation, but I think he and I agree that that's basically what it came down to. (His book: Warlord: No Better Friend, No Worse Enemy.)
Key passage here:
"In April 2004, Pantano killed two unarmed Iraqi detainees, twice unloading his gun into their bodies and firing between 50 and 60 shots in total. Afterward, he placed a sign over the corpses featuring the Marines' slogan “No Better Friend, No Worse Enemy” as a message to the local population."
You might be sick of the Dems because you don't think they play hard enough hardball with Wall St. or because they drag their feet on DADT, but it's an important reminder of what you get when you don't support them.