The new assignment, known internally as Operation Moonlight, diverted agents to a rural area outside the southern Maryland town of La Plata, nearly an hour’s drive from Washington. Agents were told that then-Director Mark Sullivan was concerned that his assistant was being harassed by her neighbor, the three people said.

Two agents were sent twice a day, in the morning and the evening, to monitor the home of the assistant, Lisa Chopey. The trips began June 30, 2011, and extended through the summer before tapering off in August, according to people familiar with internal shift records…

Agents inside the Washington field office were concerned that Operation Moonlight increased security risks to the compound and the president, two people familiar with the discussion said.