Sen. Barack Obama (D-Ill.) earned the dubious honor last week of getting Secret Service protection at the earliest point in any presidential campaign (other than former first lady Hillary Rodham Clinton, who kept her detail after leaving the White House). But at least when he’s on Capitol Hill his security world won’t be turned upside down too much.

“The Capitol Police really have the primary [security] responsibility while on the Hill,” Senate Sergeant-at-Arms Terrance Gainer, who also serves as chairman of the Capitol Police Board, said Friday. Gainer added, however, that Obama’s new Secret Service detail will be working in unison with Capitol Police officials as the Senator continues to go about his duties on the Hill.

“In general what happens when there is Secret Service protection for anybody, they work very closely with Capitol Police,” Gainer said. The Secret Service agents “understand the rules of the chamber. They are full partners. [However], access in some places is limited only to Capitol Police officers.”

Gainer declined to discuss what those locations are.

Homeland Security Secretary Michael Chertoff authorized Obama’s new protective detail last week after a request was made by Obama’s campaign, a DHS spokesman said Friday.

The spokesman declined to discuss specifics of Obama’s security detail or the nature of discussions with other law enforcement agencies that led to Chertoff’s decision.

Gainer, who previously served as chief of the Capitol Police, said that rarely does one specific threat trigger the assignment of a Secret Service detail.

“It’s really threat driven, but based on the totality of the circumstances,” he said.

Gainer said the Office of the Sergeants-at-Arms and the Capitol Police “have a very, very good working relationship with the Secret Service.”

He said that relationship hasn’t been formed just through details assigned to Members such as Sen. Clinton (D-N.Y.), who as a former first lady is provided Secret Service protection.

“It’s the day-in and day-out visitation of dignitaries and inaugurations or State of the Unions. So we work well together and understand each other very well,” Gainer said.