At one of Germany's busiest cargo airports, a drone armed with explosives was found resting quietly between two aircraft — a discovery that has since unsettled an entire nation's sense of safety. Three weeks later, a survey of more than two,000 Germans revealed that the incident had done something beyond alarming the public: it had exposed a deep and widely shared doubt about whether the country is prepared for the threats now arriving from the sky. The drone was found, but its arrival — and the silence around who sent it — has proven harder to contain than the device itself.