Can a new commander improve the dire situation in Afghanistan?

McChrystal is out, Petraeus is in. Civilian authority is reasserted, with no real compromise to the military mission. Good news, masterfully played.

Now what? Or, to put it more crudely, so what?

Yes, Gen. David Petraeus, who will be taking over command of U.S. forces in Afghanistan, is a brilliant soldier, one of the rare and true strategic thinkers in the military today. But the description also matches Gen. Stanley McChrystal, the man Petraeus is replacing.

As President Barack Obama said in his Rose Garden announcement on Wednesday, it's a change in personnel, not in policy.

The question is whether a new commander (or even slight modifications to the policy, if some are ordered) can have much impact on the course or outcome of the war. The question is whether anything can be done about the "bleeding ulcer," as McChrystal recently called it, of Afghanistan.

There are certain aspects of this war that can be changed, and Petraeus may be defter than his predecessor at addressing them. But the fundamental challenge—the chief obstacle to success—may be beyond anyone's control.

That challenge-obstacle, by all accounts, is Afghan President Hamid Karzai. In most kinds of wars, this would be a serious matter; in a counterinsurgency campaign, it's nearly fatal.

Counterinsurgency wars, as has been said countless times, are fought by, with, through, and on behalf of the host country's national government. The idea is to provide security, so the government can bring its people basic services. If the government is incompetent, corrupt, or widely viewed by the people as illegitimate, then a counterinsurgency campaign—no matter how brilliantly planned or valiantly fought—is futile.

David Kilcullen, a former adviser to Petraeus and one of the leading authorities on the subject (his much-acclaimed books include The Accidental Guerrilla and a collection of essays called, simply, Counterinsurgency), put it this way in a phone conversation today: "Counterinsurgency is a delivery system for civilian capacity. You need both. One without the other is useless."

The U.S. military is doing its part; the Afghan government isn't. The question, then, is whether the war is useless.

Take the ongoing campaign in Helmand province. In March, Gen. McChrystal moved 15,000 Marines into Marja, a Taliban stronghold in southern Afghanistan, with the goal of killing or sweeping out the insurgents, then moving in what he called "government in a box."

Two things went wrong: First, the Taliban, though initially swept out, kept coming back, especially at night. Second, and more to the point, the government-in-a-box never arrived. It never existed in the first place, in part because an Afghan government—of which this was to be a mobilized chunk—doesn't really exist, either.

Polls suggest that the Taliban are not popular among the Afghan people. They have made inroads in recent years, however, because they provide security, services, and justice—cruel forms of all three, but that's more than the Afghan government has been able to offer.

The U.S. military is stepping up to provide the security, at least in key areas. The international community can help provide the rest (and it is, with billions of dollars and a growing cadre of aid workers), but the Afghan government has to take the lead—and it's not.

So do we have a chance in hell of succeeding? "We've got a chance in hell," another U.S. adviser in Afghanistan (who asked not to be identified) told me today, adding, "That's about all we've got."

There are two preconditions for this chance in hell coming about, the adviser said: "Karzai has to be switched out or have a come-to-Mohammad moment."

"Switching him out" is not likely to happen, at least by U.S. hands. There may have been a chance to go this route just after Karzai's win in last year's fraudulent election. But once the dust settled and viable rivals failed to appear in the wings, the Obama administration realized there was no choice but to embrace him. (More direct techniques were rejected; one of the few enduring lessons of the Vietnam War is that the CIA-backed coup against Ngo Dinh Diem in 1963 didn't alter the dynamic and only deepened the quagmire.)

And so everyone is waiting for Karzai's revelation. Can one be induced? Maybe, but his regime is so entwined with corruption—at every level, among ministers, governors, police chiefs, and more—that few hold high hopes.