The opposition reads the New York Times. They've studied history, and they know all about the Tet Offensive. They are not fighting to achieve a military victory, they are murdering Americans to achieve a political victory. To do that, they need only provide grist for the Democratic anti-war mill.
In other words, American troops are dying, because the Iraqi opposition understands that Clark/Dean/Daschle/Gephardt et al will reliably use those deaths to try and sway public opinion against the war.
American soldiers are dying because the democrats view their own political fortunes as more important than U.S. security, and more important than the lives of those who risk everything to protect it.
Exactly like the RATS did to Nixon in Nam.