America may be on the verge of the most dangerous phase of the war in Afghanistan - shifting toward having its own military personnel take on high-risk operations, rather than relying heavily on Afghan proxy troops.
The reason for the change: The interests of America and its Afghan allies are diverging.
At first easy partners in the campaign to rout Afghanistan's ruling Taliban, US and anti-Taliban forces now find the partnership to be more complicated - and less focused on US goals.
Afghan warlords, always unpredictable anyway, are suddenly more preoccupied with consolidating power and territory - and may even be directing US bombs onto their rivals. And in Kabul, the fledgling national government faces pressing concerns such as setting up a telephone system and a functioning central bank.
The top US priority, by contrast, is still killing or capturing Taliban and Al Qaeda leaders.
This gap is forcing a new self-sufficiency among American forces - as well as raising the possibility of a backlash against US involvement and perhaps even higher American casualties. The growing US military presence, after all, makes for a bigger target - and the pursuit of Al Qaeda and Taliban leaders through the untamed countryside or, possibly, booby-trapped caves is fraught with peril.
"Alliances last only as long as common interests do," says Mackubin Owens, a strategist at the Naval War College in Newport, R.I. The divergent interests in Afghanistan mean "this might be one of the more dangerous parts of the war" for American forces.
The different goals are creating some tensions, which are evident in recent war developments.
Some 200 US marines recently finished what is apparently the biggest ground operation so far - a two-day trip through southern Afghanistan to survey a deserted terrorist camp.
Afghan concern is growing about US bombing - especially over the reported killing of as many as 100 civilians in the eastern region of Paktia last weekend.
This week, Hamid Karzai, chairman of Afghanistan's interim government, expressed concern about US bombs. Mr. Karzai is in a Catch 22 - between backing US goals and giving voice to growing Afghan criticism. "We want to finish terrorists in Afghanistan ... completely," he was reported as saying. "But we must also make sure our civilians do not suffer." The Pentagon doesn't rule out civilian casualties, but cites previous exaggerations of such deaths.
Concern is mounting that certain US-backed Afghan warlords are using ties to America's military to call in bombs to drop on their rivals. One commander in particular - Pacha Khan Zadran - is arousing suspicion. He denies any such activity.
True or not, in general the US is dealing with the equivalent of "feudal barons" who are asserting their power and making and breaking alliances, says David Tretler, a strategist at the National War College here. In a "Middle Ages" place like Afghanistan, where local commanders and local politics dominate, the US must find a way to operate amid tangles of shifting alliances.
The question of whether to send big groups of American forces to search Tora Bora caves also illustrates the complexities on the ground. Special Operations Forces are now working alongside some local fighters, but US officials are said to be enticing local commanders to search more vigorously by offering money, weapons, and cold-weather gear. It betrays a US reluctance to do the job - which is dangerous and time-consuming. But the commanders aren't especially motivated to do the work, and the US may ultimately have to go it alone.
Tensions are rising, too, over negotiations for the surrender of Mullah Mohammed Omar, the Taliban leader. One local commander says he's now bartering for Mr. Omar's surrender. But US officials worry that, in the meantime, Omar is getting away. Yet absent a major ground presence, the US has little choice but to rely on go-between negotiations.
More US troops are expected to arrive in the region - an influx that would allow US commanders to search independently for Taliban and Al Qaeda affiliates.
Yet the problem with a higher-profile US role is clear: The longer the US is in Afghanistan, the more potential exists for anti-American sentiment to grow - and for Afghans to blame the US for any lack of progress as their nation attempts to rebuild. "There's the possibility that our presence will become more galling, even to our allies," says Mr. Owens.
With leaders such as Omar and Osama bin Laden at large, the looming question is how far the US should press on, if it means going on virtually alone. Finishing the job will be "really, really hard," says Mr. Tretler. It could require "essentially occupying Afghanistan for a while."