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Secret Service spokesman Ed Donovan said daily patrols were sent to the employee's home during the 2011 Fourth of July weekend while the president was at Camp David.
Donovan said the units were drawn from the agency's so-called "Prowler'' unit, which he said are not part of the White House's protective detail.
"A Washington field office vehicle, an investigative asset, was used to do these periodic checks,'' Donovan said. "Because there were no protective assets used during these checks, there was no impact on protective operations.''
The patrols were first disclosed by the Washington Post, which reported that the checks went on for about two months at the rural Maryland home of Lisa Chopey, then an aide to former Secret Service Director Mark Sullivan, and included more elaborate surveillance of the neighborhood. Chopey could not be reached for comment Sunday.
The Secret Service, however, maintains that the patrols lasted only four days during the holiday weekend and involved brief "drive-by'' checks on the employee's welfare.
"Prowler has no specific assignment or protective function during movements by any protectees,'' Donovan said, adding that the units are often directed to interview suspects and witnesses and assist other area law enforcement officers.
"Prowler is not part of any protective plan,'' he said.
The disclosures come following a series of incidents that have raised questions about the conduct of agents and the agency's leadership.
In March, three agents were sent back to the USA in advance of President Obama's trip to the Netherlands after a night of heavy drinking in which one of the agents passed out in a hotel hallway.
Two years ago, the agency was rocked by a prostitution and drinking scandal involving several agents in Cartagena, Colombia, while preparing for a presidential visit there.
Secret Service Director Julia Pierson, the first woman to serve as the agency's director when she was appointed in 2013, was chief of staff to Sullivan when the patrols were authorized. But an agency official said that neither Sullivan nor Pierson was involved in directing the welfare checks.
Nevertheless, House Intelligence Committee Chairman Mike Rogers, R-Mich., said Sunday that the new disclosures raise new questions about the agency's leadership.
"They are going to have some explaining to do,'' Rogers said on CBS' Face the Nation.