Afghanistan is always compared to America's other lost war in Vietnam. That war was inherited from the French around 1962-3. President Kennedy had already expressed a apprehension and reluctance in sending anything more than a few hundred advisors. President Johnson did the opposite and sent thousands in 1965-69 in a vain effort to halt communism from North Vietnam (supported by Russia and China). In the end, the Paris Peace negotiations were a farce and a delaying tactic by the North. It dragged on for over a year as the North built up their forces with mostly Russian equipment, tanks, and artillery. When the final American forces left by the end of 1973, the South Vietnamese Army stood alone and well equipped. But the problem was not their equipment or numbers, it was their morale, their willingness to fight for their freedom. When the North attacked in 1974, the weakness became apparent. Then, in 1975, the South just melted away when the massive attack occurred. It was all a wasted American effort.
Afghanistan is very similar, but it is a 20 year war! Once we got our man, Osama Bin Laden, things did not change. The US continued to fight and try to save Afghanistan from the Taliban, a very backward culture dominated by men. The US mission was to stop them, stop terrorists like ISIS. Like the Russians in the 1980's, who finally fled after eight years of trying to make them communist, America has tried to make them a democracy. There are successes. Not all is bad. But, in the end, which is coming in 2021-2, will the Afghan army be any different than the South Vietnamese Army?
Even now, reports are coming in that when this army is facing the Taliban, some units just surrender, which is why most of the provinces outside of Kabul are in Taliban hands. The Afghan Army's morale is paper thin and only decent if the Americans were supporting them (just like in Vietnam). The pendulum is swinging the Taliban way as more provinces are taken, the more loss of morale in the people and Afghan Army. Even if their army is able to hold onto an island province of Kabul, it is just a matter of time until the whole defense erodes and collapses. Having remote American support will have little impact since the time to get there from far away bases makes it near pointless.
Did America lose this war? What is winning in Afghanistan? You cannot defeat the enemy in 20 years, there is a reason to cut your losses. If the Afghan morale is so poor that they cannot stand up to a weak force, then, like Vietnam, its pointless to go on. But Biden's error is not leaving some US soldiers on the ground to help with transitioning, instead, they vanish in the middle of the night as if they are afraid also. That is very bad on Afghan morale, seeing their mentors bail out without any notice.
The Taliban are not waiting. They continue to take one province after another, freaking out the Afghan army and population in Kabul province, in another time, it was Saigon. Like in that other war, there will be a bitter and brief battle in and around Kabul with the best Afghan troops making a stand. But it will end sooner than later just like in that other war America lost.