Undersecretary for management Patrick Kennedy unexpectedly stepped down after nine years in his role, and Assistant Secretary of State for Administration Joyce Anne Barr, Assistant Secretary of State for Consular Affairs Michele Bond and Ambassador Gentry O. Smith, director of the Office of Foreign Missions, all followed suit. The four officials, who have served under both Republican and Democratic administrations, are charged with managing the agency and overseeing its staff diplomatic posts abroad.

Kennedy was actively working to assist Donald Trump’s transition team and his departure came as a shock to current and former foreign policy officials, according to the Post. It follows the Jan. 20 resignation of Assistant Secretary of State for Diplomatic Security Gregory Starr and director of the Bureau of Overseas Building Operations Lydia Muniz.

“It’s the single biggest simultaneous departure of institutional memory that anyone can remember, and that’s incredibly difficult to replicate,” David Wade, State Department chief of staff under Secretary of State John Kerry, told the newspaper. “Department expertise in security, management, administrative and consular positions in particular are very difficult to replicate and particularly difficult to find in the private sector.”

If confirmed, President Donald Trump’s pick for secretary of state, Rex Tillerson, will begin his term without the assistance of career civil servants who can help him navigate the inner workings of the agency. Tillerson, the former CEO of ExxonMobil, has no experience working in government. He was approved by the Senate Foreign Relations Committee on party lines, and is expected to be confirmed by the GOP-controlled Senate.