Why did Saakashvili try this now? — Here’s my guess, based on my impression of Saakashvili’s character.

Saakashvili is an ardent nationalist who doesn’t view the disputes with Russia rationally. To him, they’re painful and continuing insults to the national soul.

More importantly, Saakashvili is a gambler.

South Ossetia has always been vulnerable to a blitzkrieg attack. It’s small, it’s not very populous (~70,000 people), and it’s surrounded by Georgia on three sides. It’s very rugged and mountainous, yes, but it’s not suited to defense in depth. There’s only one town of any size (Tsikhinvali, the capital) and only one decent road connecting the province with Russia.

That last point bears emphasizing. There’s just one road, and it goes through a tunnel. There are a couple of crappy roads over the high passes, but they’re in dreadful condition; they can’t support heavy equipment, and are closed by snow from September to May. Strategically, South Ossetia dangles by that single thread.

So, there was always this temptation: a fast determined offensive could capture Tsikhinvali, blow up or block the tunnel, close the road, and then sit tight. If it worked, the Russians would then be in a very tricky spot: yes, they outnumber the Georgians 20 to 1, but they’d have to either drop in by air or attack over some very high, nasty mountains. This seems to be what the Georgians are trying to do: attack fast and hard, grab Tsikhinvali, and close the road.

Small, weak states living next to abrasive, unpredictable great powers need to be extremely careful about what they do; in most cases, their foreign policy should, first and foremost, be about avoiding war with the great power. This is what Saakashvili failed to do. The war didn't need to escalate; it was a Georgian decision to move from the village skirmishes that were happening on Tuesday to the siege of Tsikhinvali on Thursday.

It looks right now as if that strategy has failed. The Russians seem to have been able to deploy a substantial armored force in South Ossetia, and also seem to control the sky. Of course, we don't know what things will look like tomorrow, but right now they don't look good for Georgian efforts to close the road. And if the Georgians can't close the road, they are in very serious trouble. Indeed, even if they do close the road they might be in trouble; the other way that the Russians might get into South Ossetia is to go through Georgia. That would be an escalation, but the Russians might be tempted by their overwhelming theater superiority, and by the stakes.

The stakes for Putin and Medvedev are also extremely high. I think that they could have given up on South Ossetia without taking a severe domestic hit; their popularity is solid, Russia is still making plenty of money (even with oil dropping), and Abkhazia has always been the more important of the two frozen conflicts. Now that they're committed, however, I suspect that it will be very hard for Putin and Medvedev to disengage. It's war; anything can happen, and if the Georgians somehow manage to pull it out, it's a political disaster for the Russian leadership. The Putin dynasty's legitimacy is based around the idea of Russian national resurgence, and if a ridiculous little country like Georgia manages to give the Russian Empire a bloody nose and get away with it, Putin and Medvedev become vulnerable. This, I think, is the most dangerous part of the crisis for Georgia. Russia will pull out the stops to win this war; if they can't win easy, then they'll win hard, because Russia's leadership really doesn't want to be beaten.

Saakashvili also can't afford to lose. He came to power in a landslide victory in 2004 promising to bring back the rebel provinces. But as Russia has grown more oil rich and assertive, so Moscow's diplomatic and practical support for the breakaway Georgian enclaves has grown—and the chances of Tbilisi ever recovering them has shrunk. Most citizens of Abkhazia and South Ossetia have been issued Russian passports and are eligible for Russian pensions; in April, the Russian Duma passed a law authorizing official ties with the rebel republics. At the same time, NATO caved in to Russian pressure and declined to give Georgia the clear invitation to membership it had sought. "The message Saakashvili got from that was: it's now or never," says one senior Western diplomat in Moscow not authorized to speak on the record. "The assault [on Tskhinvali] was a gamble."

It's a gamble that could backfire badly. Saakashvili may have made exactly the mistake Russia wanted him to make—giving Kremlin hawks the excuse to fill Ossetia with Russian tanks, bloody the Georgian Army's nose and destroy his chances of re-election. Saakashvili's appeals to the West for help are unlikely to elicit any practical response, other than diplomatic hand-wringing. There's little doubt that tiny Georgia has little chance against the might of the refurbished Russian Army in an all-out war. So far, one of the brightest young leaders of the former Soviet space is set to destroy the other.

Russia gets to demonstrate her power, solve two of the Frozen Conflicts (the Georgians are never getting Abkhazia back if Russia wins here), and humiliate the United States, all at the same time. They hit the trifecta if they win this war.

If the war develops as expected, and Russia pounds Georgia until the latter cries uncle, the United States will have suffered a substantial political setback. Hegemony or no, the United States will have been unable to give significant military aid to an Iraq War ally facing the prospect of interstate war. This isn't the end of the world, but it's not great.