Afghanistan is on the brink of chaos: That is the stark message from local leaders, the US military and development workers in the troubled country. The elected government, they warn, can no longer compete with the Taliban.

On the Red Bridge across the Red River, protected by watchtowers on both sides, Mohammed Halim Fidai orders his convoy to stop so that he can take a short, symbolic walk through enemy territory 50 kilometers (31 miles) west of Kabul. His three Toyota pickups, with machine guns mounted on their beds, block Highway One at the front of the convoy, while another three Toyotas bring up the rear in the snow-covered landscape. Policemen, their weapons at the ready, fan out, forming a cordon around Fidai.

Fidai, who is the governor of...