The entire senior level management team at the State Department was fired by President Donald Trump’s administration this week, CNN reported Thursday.

Senior administration officials told CNN’s Elise Labott that four top State Department staffers were informed in letters sent by the White House that their service was no longer required. The pro forma resignation letters typically submitted by the heads of federal agencies at the start of new administrations were accepted.

The Washington Post previously reported that undersecretary for management Patrick Kennedy stepped down unexpectedly Wednesday 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.

“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.

This post has been updated.