ISLAMABAD, Sept. 25 -- Three of Imran Khan's sisters are sitting in a Lahore jail tonight, held under a colonial-era law that requires no charge and no trial, signed off by a district official in thirty minutes. The motorways leading into the capital have been sealed with shipping containers stacked two stories high. And the march they were all arrested to stop is still three days away.

Pakistan's government has deployed roughly two thousand containers across every major highway from the northwest, the region where PTI commands its deepest loyalty. The motorway to Peshawar has been closed entirely. The Grand Trunk Road at Attock bridge, the crossing that links Khyber Pakhtunkhwa to the rest of the country, is impassable. The Hazara motor...