The argument for leaving is laid out in Trump Wants to Fire U.S. Commander in Afghanistan, in which I explained that the unsolvable part of the Afghan problem is civil, not military. Quoting,

The bare-bones boiled-down essence of modern government is just a few things:

• • Raise revenue by taxation.
  • Use at least some of the taxes to provide services.
  • Facilitate commerce.
  • The services provided justify the taxes enough for popular acquiescence.

You can add all the bells and whistles. But it’s the irreducible minimum. Anything less, and it becomes a protection racket.

Afghanistan has no legitimate economy.

Hence there is no way for the legitimate government to differentiate itself from the Taliban, save social values, which are not enough. We could stay there forever, as Lindsay Graham advised Trump. But when forever is over, the result would be the same. Liza Minnelli: Money makes the world go around.

(The Hill) Top general: Counterterrorism strikes in Afghanistan after withdrawal ‘harder’ but ‘not impossible’ Quoting ,

On Tuesday, [Gen. Frank] McKenzie also said he continues to have “grave doubts” about the Taliban’s reliability in upholding its commitments under the deal signed last year.

I have grave certainty that they won’t uphold. This will be a slaughter of the good. The   future reeks of the fall of Saigon, when our friends were falling off helicopter skids as they begged for rescue. I suspect that the slaughter of innocents bothers H.R. McMaster even more than the strategic retreat.

To remain would only delay the inevitable. Afghanistan is caught in the gyre of a primitive cultural ocean.  Eventually, China, and perhaps India will, in exploitation, bring some measure of humanity.

A legacy of attitude promotes Indefinite commitment. In 2001, the U.S. was the unchallenged superpower. Now it is challenged. We are not quite through that era, but we can see the sunset. Now, we must prioritize.

With the withdrawals, ceding large territories to the Taliban, costs are down. The cost of regaining control of the country approximates the $100BN/ year peak costs. But the budget bleed is not the deciding factor.

Afghanistan is not supplied by a sustainable air bridge. For gross tonnage, we rely on Pakistan, which has strong ties to China. The other bordering states are potential, if not actual, adversaries. U.S. troops could be isolated as hostages if hostilities occur elsewhere. Our presence in Afghanistan interferes with credible deterrence elsewhere.

This is not hawk versus dove. Most military, particularly those who are familiar with the hard truths of simulations, know this: A superior military can be destroyed by over-extension.

To those who idealize the U.S. posture without thought of strategic balance, there’s always common sense:

You don’t go into a gunfight with your nuts hanging out.