In the upcoming debate in Congress on the war in Iraq, Republicans are going to want to focus solely on the progress being made in al-Anbar province. Democrats are going to want to focus solely on the lack of political progress in Baghdad. But what could prove to be the tipping point in the debate is what the British are currently focused on: Basra. Because what happens there, in the next few weeks, may determine the outcome of the debate in Washington.

First, a little background on the military situation in Basra. To begin with, the British armed forces have been in charge of the southern region of Iraq since the war started. They were originally in charge of four whole provinces, and also in charge of the training programs (of the Iraq military and police) within their region. Three of these four provinces have already been successfully turned over to Iraqi military control. The remaining province -- Basra Province -- is still under British control, as is the city of Basra itself.

The Brits made the news a few days ago by announcing that they were pulling out of the city center, and will now consolidate all of their forces in an airbase at the edge of town. They previously had 5,000 forces at the airbase, and 550 more stationed in a former palace in the middle of Basra. The palace and (to a lesser degree) the airfield, have been under constant attack from Shi'ite militias. The news was that the 550 in town are moving out (with all of their equipment) to the airfield, and that the city itself is now under Iraqi control. Now, that's supposed to mean "under Iraq's Army and police control," but it's actually an open question whether it's really going to mean "under Shi'ite militia control." To further complicate the situation, there is more than one Shi'ite militia group battling for control of the city, so even "which Shi'ite militia" will be in control is also an open question.

The United Kingdom, it should be pointed out, just got a new Prime Minister. And the new "P.M." is there because he swore he wouldn't behave like Tony Blair, who reduced the U.K. to being ridiculed as "America's poodle." The British press is speculating like mad that the pullback by the British forces in Basra city is a precursor to the U.K. pulling all of their troops out "in the fall" (which, it should be pointed out, is not so very far in the future). The U.S. media is reluctantly covering the story, but is not really spotlighting the fact that our longest and best ally in Iraq is about to get out of Dodge for good.

But the real story is that we're about to see a microcosm of actual hard data in answer to the question: What will happen when the U.S. leaves Iraq?

This is a question that deserves attention. Much more attention than it is currently getting. All of America, including all her politicians, are focused on only two questions right now: has the "surge" worked; and when will we begin to leave? But the more important question for the long-term consequences in the region is: What exactly is going to happen when we do get out?

Until this point, anyone speaking both honestly and realistically about Iraq's future has had to answer this question by saying: "Nobody knows." Sure, speculation on the subject abounds, but no one in their right minds could (or would) state without a shadow of a doubt that "this is what is going to happen when we leave" -- no matter what "this" happens to be.

Of course, Democratic supporters of Joe Biden's candidacy for President become almost apoplectic when this question is raised, because (as they will earnestly tell you): "Joe's got a plan!" Now, I'm not an official supporter of any Democratic candidate (I'm still waiting for someone to hire me to write their speeches... ahem), but I have to say the Biden crew is absolutely right on this issue -- Joe Biden has actually thought about what is going to happen "next" in Iraq, and he has what he believes is a solid plan to have a positive outcome.

I mention this because everyone else (both within the presidential race and without) doesn't really have a better idea. Or any idea, for that matter. Biden's plan may not be the best idea, or (conversely) it may be the perfect idea, but at least he's thought about it, and at least he is willing to publicly propose something -- and (by doing so) stake his own political reputation on it. Which is more than can be said of most everyone else, both Democrat and Republican alike.

But we are all about to get some indication of what a post-American-involvement Iraq will look like. Now, to be sure, it is not fair to judge the entire country by what happens in Basra; any more than it is fair to judge the potential benefits of the "surge" by what is happening in al-Anbar. In both cases, the argument is the same: Iraq is an incredibly complex situation, and you simply cannot take the lessons learned in one small region and apply them to such a volatile mix as exists in the country as a whole. There are such entrenched ethnic and sectarian tensions in each individual region in Iraq as to make such facile pigeonholing a fool's game.

In both cases, however, what matters is not so much the actual situation on the ground in Iraq as the perception of the situation on the ground by Americans (both politicians and the public at large). And the spin which accompanies such perceptions, of course.

Because, while the situation in Basra may not be such a strict dichotomy, this is how it will be presented to America: either Basra is still doing "OK" in two weeks' time; or, alternately, it has descended into complete chaos and anarchy.

Depending on how things go, and how it is all spun, this may prove to be the trump card in the upcoming debate. Which is why the news from Basra demands close attention for the next few weeks.

If Basra is complete chaos and anarchy, a true Hobbsian state of "all against all," with no clear winners and constant fighting in the streets -- then it benefits the Republican argument. If Basra is basically doing OK without the British -- then it bolsters the Democratic argument.

Because the argument for continuing both the "surge" and the continued presence of the American military in general boils down to this: if we leave sooner, rather than later, will that help or hurt the Iraqis -- and Iraq itself -- in the long run?

Republicans are already painted into President Bush's corner in this argument. Their position is that Iraq will fly apart and descend into a violent bloodbath if we leave too soon. The Bushian argument: American presence, and indeed the "surge" itself, is all that is holding back complete chaos -- and the only way we'll prevent such chaos is if we stay long enough to allow reconciliation to take place so that the various factions in Iraq won't want to kill each other (as much) when we eventually do leave.

Democrats are harder to pin down on what they believe, due to the normal "herding cats" nature of figuring out what Democrats actually will stand up for. Their basic stance (I guess) can be summed up as: Iraq is going to have a civil war whether we're there for it or not. Because more American soldiers will die if we try to stay and police it, we should cut our losses and get out now. Or maybe the Democratic position is: nobody knows what will happen if we leave Iraq now, and all these fears of bloodbaths may be overblown; because maybe our presence is the main problem, and just maybe -- if we leave -- things will calm down afterwards.

One last thing worth mentioning is that Basra is strategically important, no matter what the outcome. Militarily, Basra (and the surrounding region) is a key part of the supply lines to Baghdad (and the rest of Iraq) from the U.S. military's staging grounds in Kuwait. If the region flares up when the British pull out, it will mean American soldiers are going to have to secure these supply lines -- perhaps at great cost.

The other reason Basra is strategically important is that it is the one port Iraq has to ship its oil out to the rest of the planet. The pipelines all end there. Which means the consequences of Basra going up in flames are indeed immense for the rest of Iraq -- and for Maliki's government in particular. If the oil can't get out, then the Iraq government loses a LOT of money that they are counting on.

The timeframe is tight, because the Iraq debate in Washington is going to occur in the next few weeks. So even if initial reports aren't an accurate prediction of the ultimate outcome in Basra, the next few weeks may be the straw which breaks one camel's back or another.

If Basra goes up in flames, look for Republicans in Congress to bludgeon Democrats with the following: "See?... SEE?!?... We TOLD you this would happen if the coalition pulls out too early! This is what's going to happen to the WHOLE COUNTRY if we withdraw now, right when we're on the verge of success in Iraq."

If Basra remains calm and the Iraqi forces contain things well enough to keep chaos off American network news television screens for a few weeks, look for congressional Democrats to (hopefully) use the opposite argument: "See?... SEE?!?... We TOLD you that all your fears of utter chaos are unfounded because OUR PRESENCE in Iraq is the main cause of all the violence. Once you remove the coalition from the field, things will improve in Iraq. Our success depends on us getting out as fast as possible."

I have to admit that I have no magic crystal ball. I cannot predict which outcome will happen in Basra from such a distance, and at such remove. I truly have no idea how it will happen, or how it will be presented to Americans on their nightly news... or (perhaps more importantly) how it will all be spun by the politicians. Nobody outside of the U.K. seems to be paying much attention to Basra. That may change soon, as conditions on the ground warrant.

But while I admit to no prophetic powers myself, I am smart enough to make one major prognostication:

Watch Basra.

Because as goes Basra may go the entire Iraq debate in Washington.

Cross-posted at The Huffington Post

-- Chris Weigant