Daniel Drezner expresses doubt about a prediction in the far-rightist American Conservative magazine that Iraq will be for the US what Lebanon was for Israel. Michael Desch suggested that American troops in Iraq may find themselves in a Vietnam-style "quagmire", taking steady casualties in an unwinnable war against an invisible guerrilla adversary. Drezner thinks this scenario unlikely, but does consider it "a possibility", and suggests that "[t]he Lebanon analogy is a useful one to remember that things in Iraq have the potential to turn sour."
To understand whether and how the "Lebanon analogy" may apply to Iraq in the future, it's important first to understand just what happened to Israel in Lebanon. The situation there was very much analogous to America's in Vietnam: Israel's enemy, Hezbollah, was able to take advantage of an adjacent sanctuary (Syrian-held territory in Lebanon) where for political reasons Israel's counteroffensive operations were severely limited in scope. Israel was also unable, for both political and logistical reasons, to seal off its occupied zone from the Syrian-controlled sanctuary. The result was predictable: Israeli soldiers were sitting ducks for Hezbollah attacks--shelling, ambushes, raids--launched by guerrillas based in the sanctuary, against whom the Israelis were unable to respond effectively.
The lesson for the US is clear: the danger to occupying American forces is not from Iraq proper, but from hostile neighbors--Syria and Iran. Syria is probably too weak and vulnerable to be a threat, but it's entirely possible that armed "resistance" groups, trained, equipped and based in Iran, might begin slipping across the border and launching regular attacks on US forces in Iraq. I just hope the latter have the means--and the political green light--to deal with that contingency, should it come to pass.