The article below offers some interesting comments by former U.S. Ambassadors Ryan Crocker and Ron Neumann. They focus on lack of State-DoD coordination and shortcomings in public diplomacy efforts.
"The tone of these experienced diplomats was quiet anger about the decision to pull out of Afghanistan, which they attributed to the last two administrations. And grim pessimism about a true reckoning that might prepare the U.S. for future crises."
"Lessons from Afghanistan - Two Ambassadors Speak" - Public Diplomacy Council