Even as he prepares for a potential White House bid, Maryland Gov. Martin O’Malley (D) is continuing to lose key State House staff, a phenomenon typical for a governor nearing the end of his tenure.

The latest to depart for the private sector is Rebecca Mules, one of O’Malley’s legislative lobbyists in Annapolis who had been his longest-serving aide still on the government payroll.

Mules signed up with O’Malley in 1999 during his first campaign for mayor of Baltimore and had worked for him ever since. For much of that time, she served as O’Malley’s scheduler, in Baltimore and later in Annapolis, before moving to the legislative shop in 2011.

In an e-mail to friends and colleagues this week, Mules said that she is starting a state government relations job with UnitedHealth Group next month.

“It has been an amazing tenure with Governor O’Malley, and I would not be the person I am today without the experiences and relationships I have enjoyed these many years,” Mules wrote.

O’Malley, who arrived in Annapolis in 2007, is term-limited and scheduled to step down in January. He brought a cadre of aides from Baltimore to the governor’s office, only a few of whom remain today.

They include Jeanne D. Hitchcock, who now holds two positions: chief legislative officer and secretary of appointments. Others long-time aides staffers with O’Malley include Peggy J. Watson, a deputy chief of staff; and Jay L. Baker, his chief photographer.

Several former aides who have left for the private sector remain close to O’Malley and serve as informal advisers.