US forces are now in a precarious and untenable position in Iraq. The window of opportunity for an easy exit has passed. Three years of fighting an open source insurgency has destroyed Iraq's economy (through systemsdisruption starting in 2004), worn down US commitment/curtailed operational flexibility (the IED marketplace during 2004/05/06), and forced a country-wide descent into primary loyalties (through a combination of social systems disruption that reached a crescendo in 2006 and an early reliance on loyalist paramilitaries as a force multiplier back in 2004). Iraq is now in full failure and as a result, the assumption that the US will be able to continue with its partial efforts at urban pacification has become dangerously wrong.
The reasons should be obvious. US forces are now surrounded by a sea of militias and insurgents. Within Baghdad itself, where the current pacification effort is focused, US troops are badly outnumbered in extremely difficult urban terrain. Worse yet, the opposition is growing in numbers, sophistication, and aggressiveness at a rate more rapid than the static number of US troops can build up the Iraqi military. It is now only a matter of time before either a misstep or a calculated event pushes the countryside into full scale warfare.
In this near term conflict, we are likely to see a repeat of the lightly manned defensive hedgehog used successfully by Hezbollah against Israel. That lesson was not lost on this war's open source participants, particularly Sadr's Mahdi Army, which uses Hezbollah as a model (which implies they might try to replicate Hezbollah by translating success on the battlefield into the critical currency of "legitimacy"). If placed along critical US military supply routes or immediately outside US mega-bases, and augmented by informational superiority (a combination of better local intelligence and advanced signals intercepts), these defensive tactics would extract a heavy toll on US troops (even as the US wins a tactical victory). Further, if repeatably successful, these efforts will force the US to forgo all efforts at offensive pacification operations in favor of basic force protection (not only for US troops, but the tens of thousands of civilians on these bases). From that point on, the timer will be on until a US forward base is overrun (when it finally goes off, we will be cooked).Of course, the above outcome grows increasingly likely as the rhetoric for a war with Iran heats up, given that Iran can easily supply the weaponry necessary for these tactics. Since the current US administration's timeline for this new war isn't Iran's nuclear development cycle, but rather the US '08 election cycle (because they don't trust the next administration to make the tough decisions on the issue), this may come into being soon.