Americans are genuinely surprised that the Taliban conquered Afghanistan in six weeks. Perhaps that is because they believed the stream of evasion emanating from the government for an entire generation that the war against the Taliban had been won (or close to it) and the U.S. was simply taking its time leaving the country.
It would be easy to blame Joe Biden for condemning thirty-eight million Afghanis to a tyrannical future under Sharia law enforced by genocidal maniacs, but Biden simply played the last move that remained on the board. The game was started four presidents ago and each of them played moves toward the disastrous endgame for which Biden will take the blame.