Why are they winning?
Senior US officers and White House officials insisted before the withdrawal began in May that the Afghan police and army were up to the job of defending themselves. They were clearly wrong.
At least part of the problem seems to be morale. While special forces units continue to fight, regular troops in many places appear to have withdrawn voluntarily or accepted offers to surrender, allowing Taliban fighters to roll into towns unopposed.
Others argue that is partly due to a loss of hardware and capability.
Tom Tugenhadt, a Conservative MP and former soldier who served for four years in Afghanistan, argues Afghan troops have been cynically deprived of the battle-winning technology Western forces taught them to rely on.
“The decision to withdraw is like a rug pulled from under the feet of our partners. No air support, none of the maintenance crews able to service their equipment – that was done by US contractors, now gone,” he wrote on Thursday night.
“Training a man to fight with his eyes open and then blindfolding him before his title bout is going to have only one result.”
Where are they getting their kit?
Somehow, the Taliban has been able to deploy a well-planned nation-wide offensive, with simultaneous operations at opposite ends of the country.
And they suddenly appear to have no shortage of men, weapons, ammunition, or fuel.
Some of those resources will be self-funded. The Taliban make a lot of money from opium smuggling, and as the offensive rolls on they have captured an increasing quantity of American kit abandoned by government troops.
There are also reports of jihadi fighters from neighbouring countries bolstering their ranks.
But is that enough to explain their recent success? Many Afghans and Western observers also place the blame squarely on Pakistan.