"We don't comment on our protective operations," a spokeswoman for the agency, Catherine Milhoan, said.
In total, the Secret Service spends more than $750 million of its $1.8 billion budget on protective operations.
The departing assistant directors headed up divisions covering protective operations, investigations, public affairs and technical development.
"Because there were no protective assets used during these checks, there was no impact on protective operations," Donovan said.
She said he would be replaced in May by James M. Murray, a career Secret Service official who oversees protective operations.
The service had said the tours were canceled to avoid furloughs in other more critical protective operations.
Murray, the assistant director of the office of protective operations, had served as the special agent in charge of the agency's Washington field office.
Danny Spriggs, the assistant director for protective operations at the Secret Service, said the only event that compared to the Millennium Summit in terms of V.I.P. protection was the 50th anniversary celebration at the United Nations in 1995.
For example, an Oct. 9, 2003, message referring to a "Harlem Spelling Bee," ridiculing black slang, was sent by Thomas Grupski, then assistant director for protective operations, who, according to the filing, now heads the Office of Government Liaison and Public Affairs.
(Secret Service spokesman Marty Mulholland declined to comment for this story, citing the agency's policy of not talking about protective operations). But shielding Trump from harm is only one of many objectives.
