He was handed a lost war with an agreement already in place that the US would pull out. He was then left to manage that withdrawal. A withdrawal of vast numbers of people and equipment from a country whose native government and army collapsed almost immediately the US started to retreat.
So what exactly should he have done? To stop the Taliban advancing so quickly would have required military resources, the very same resources they were trying to pull out. Once the Taliban were sweeping across the country, then it was basically guaranteed to be chaos.
The abuse aimed at Biden seems to come from some strange presumption that you can retreat from a hostile country while simultaneously keeping control in that country while your forces pull out. This fantasy should have died a death after the chaos of Saigon, so I have no idea why it continues to be so widely believed. Well actually I do have an idea, which is that Americans are so convinced that their military is the ultimate force on the planet that no enemy can stand against, that they lose a bit of a grasp on reality when it comes to things like this. It turns out that having the best planes, tanks, missiles and ships doesn't actually mean you can always control anywhere you please.
