In the world of cheap drones, Skydio was the great American hope. Its autonomous flying machines gave the U.S. defense and police agencies an alternative to Chinese manufacturers, free from the security concerns tied to dependence on Chinese supply chains. But Skydio’s vulnerabilities came into sharp focus days before the U.S. presidential election, when Chinese authorities imposed sanctions and severed the company’s access to essential battery supplies. Overnight, the San Mateo, Calif.-based Skydio, the largest American maker of drones, scrambled to find new suppliers. The move slowed Skydio’s deliveries to its customers, which include the U.S. military. “This is an...