Michael O'Hanlon in the National Interest. Says essentially what I was arguing earlier. The US has abandoned its 2001-2020 nation-building game (perpetually on defensive, never having the initiative, and trapped in a situation where less than 100% success = failure).There is another possible future for Afghanistan, and while not pretty, it is strategically far preferable for the United States: a military stalemate, in which the Taliban holds some of the country and the government while friendly militias hold another big chunk.
Instead, the US is now playing a game of denial (their objective is not to control Afghanistan, but to deny control of Afghanistan to the Taliban or any power who backs it). The US faces a much lower cost of prosecuting the war and takes much less of a propaganda strike in case of any successes by the Taliban. Conversely, the Taliban is on the hook until it succeeds in capturing the whole (or almost the whole) of Afghanistan.
Now (in the war of perception, which is as important as the military conflict itself) the onus is squarely on the Taliban to gain control of the whole of Afghanistan. The US will deny it this victory using stand-off munitions and airstrikes to support the Taliban's opposition-- for now, that opposition is the ANG, but it need not always be. The approach is similar, for the moment, to the one Russia took when stabilizing the Assad regime in Syria. Don't try to liberate all of pre-2013 Syria but fight for a stalemate where the key centers of political legitimacy and economic power are perpetually denied to the Islamist insurgents.
This allows Kabila theory to be used in the opponents' favour. We had discussed this several years ago on BRF. The idea is that Kabilas (armed camps or organized militias) in the Islamic world need to maintain their supremacy and prestige with a continuous series of visible "wins", garnered at a high rate of success. From the Umayyad Caliphate to the present, a decline in the pace of wins, leading to stagnation, is the first step towards rapid decline and overthrow.
This was used in 1996 by the Pakistanis who created the Taliban to take advantage of a prolonged stalemate in Afghanistan and seize Kabul. After many years of continuous battle the earlier combatants (Gulbuddin Hekmatyar, Sibghatullah Mojadeddi, Ahmad Shah Massood etc.) had few gains to show for themselves. The very fact that Taliban were capable of winning some battles quickly, and dynamically changing the ground situation at a fast rate, made them appear unbeatable.
Of course at that time the Taliban were backed by not just Pakistan but Qatar, KSA, UAE, and tacitly the US (which was an unchallenged hyperpower back then). Now, it's mostly just Pakistan. China is trying to make some headway as a godfather of Taliban, but it remains to be seen how effective they will be... their hesitations, especially with regard to Xinjiang blowback, are considerable.
This can be viewed in contrast to the Kashmir situation. From 1990 to about 2003, Pakistan kept sending jihadis recruited from the international Islamist tanzeems to try and fight a jihad in Kashmir. They did a lot of harm and murdered many innocents, but in the end they were always killed without achieving any political goals. The Indian state never budged an inch.
After a long time of this, the "air goes out of the Kabila's tyres" so to speak. They need to push the long-drawn-out, inconclusive conflict onto the backburner and instead emphasize other conflicts where victories are easy, dramatic, and rapid (this is one reason why JeM, HuJI, and other Deobandi groups which were initially Kashmir-oriented shifted much of their focus to Afghanistan in the late '90s).
If a Kabila is seen to get stuck in a stalemate, it's in deep trouble-- other Kabilas seeking to oust it from the position of supremacy will take its place. That's why a Taliban incapable of taking over Afghanistan after the US withdrawal will find itself in an increasingly compromised position over time. They will have to take their jihad elsewhere to maintain their prestige with dramatic attacks and a quick pace of results. India has to ensure that the place they take it is KPK, Krrachi, and Baluchistan.
As for the territorial integrity of Afghanistan itself-- Biden has never been a champion of preserving that. Even as Obama's VP in 2008, he advocated for a partition between the Pashtun south and a remaining rump Afghanistan in the north. A consolidated Pashtun state may find it tough going to seize the north, especially if US B-52s and other national birds are slowing the pace of their conquests and increasing the costs. So they may well decide to look across the Durand line for a more politically expedient conquest.