The Secret Service monitored Brenda Allen and her family for months. The surveillance came after an altercation with her neighbor, who worked for former Secret Service Director Mark Sullivan.​ (Theresa Poulson/The Washington Post)

Congress’s chief oversight committee has launched a formal investigation into how and why Secret Service agents were ordered to leave their assignments protecting the White House complex to instead protect a close friend of the agency’s director.

The House Committee on Oversight and Government Reform asked Secret Service Director Julia Pierson by letter Tuesday to turn over all documents detailing how and why agents were pulled from providing extra protection for President Obama and his family in summer 2011 to go to La Plata, Md., as part of a new assignment called “Operation Moonlight.”

The Washington Post first revealed the existence of the operation, in which agents were pulled from a special unit monitoring the White House perimeter to instead check on the home of the administrative assistant of then-Director Mark Sullivan. Agents were told Sullivan had directed that they be diverted to her home out of concern that his secretary was being harassed by a neighbor, but several agents were concerned that the operation was illegal.

Committee Chairman Darrell Issa (R-Calif.) and Rep. Jason Chaffetz (R-Utah), chairman of the national security subcommittee, said the pattern of reported misconduct at the Secret Service since agents were embroiled in a 2012 prostitution scandal in Colombia has been worrisome and that potential risks to the president’s safety must be investigated.

“The actions described in these reports, if true, fit a pattern of impropriety and mismanagement at the Secret Service as seen in several recent scandals,” Issa and Chaffetz wrote. “Questions remain as to whether this course of action detrimentally impacted the President’s security.”

The Secret Service and Operation Moonlight

The Post reported this month, according to three people familiar with the operation, that agents went in shifts to visit Lisa Chopey’s home for two months; the Secret Service has said the diversion lasted only four or five days.

Sullivan told The Post through a spokesman that he did not order the diversion of agents but believed it was appropriate to check on the safety of an employee.

Chopey moved to a job at the Department of Homeland Security, the parent agency of the Secret Service, when Sullivan left the agency in early 2013. She has declined to comment on the report.