Jeffrey Gettleman has the details. The cycle of revenge will continue to escalate -- Zarqawi pulled it off (he's likely off to Jordan now, his job in Iraq is done). Here's a likely scenario: US troops, caught between a government that has outsourced security to militias and the guerrillas, will hide by entrenching themselves in their bases. That won't help. There will be attempts at intervention to prevent wholesale slaughter, but these events will only increase tensions with the militias. Eventually, these militias in combination with the guerrillas will cut supply lines to US bases. Unable to function, there will be an attempt at a belated withdrawal. It won't be pretty.