For more than a decade, the employees of a Washington think tank were traumatized by an unlikely harasser: a career Foreign Service officer. In hundreds of emails and voicemails, he called them “Arab American terrorist murderers” and ranted about how they should be cleansed. Yet there was almost nothing they could do.

The weakest link in America’s national security may not be foreign technology but its own people. The story of the single mother who sold out to China.