IMO, we should keep a force of 5-10 thousand there for the foreseeable future in order to forestall any possibility of the Taliban regaining power. Give them plenty of Airpower and a well fortified base of operations. But allow the Afghan government to run all other aspects of the country. If they can keep a relatively stable government for 20-30 years, they might actually have a shot at making it as a country.
The region's history strongly indicates Afghanistan will not be tamed by an invading empire.
Even if it were possible to recreate Afghanistan in our own image, the US should be asking itself one question: Is it worth the cost?
The risk of investing those same funds here at home would be considerably less and the rewards significantly greater.
Invest in modernizing our country's crumbling infrastructure and those dollars will move from one American to another countless times, stimulating our industrial base and reducing unemployment.
Waste funds in Afghanistan and those trillions of tax payer dollars will most likely to fall into the hands of some corrupt government official or tribal leader feathering their own nest or buying arms to kill more American soldiers.
It is interesting to me that many of the same politicians who support drastic cuts in unemployment and educational benefits, all in the name of "fiscal responsibility", don't hesitate for a second to support pouring billions into unstable, unproductive, fiefdoms filled with individuals who would rather kill us, than thank us for our efforts.
Even now, our military does not control much of Afghanistan. There is little reason to believe another 30-50 years of troops and resources will magically result in successful nation building.
Nation building in Afghanistan is nothing more than mission creep and mission creep leads to mission failure.
Eventually, our politicians will be forced to accept that Afghanistan is a futile effort. We are wasting countless American lives and resources in a losing battle to prop up a notoriously corrupt government. Just like in South Vietnam.
Hopefully, it won't take 50 years for the American people to figure that out.