The head of the Department of Energy division responsible for overseeing and maintaining the U.S. nuclear weapons arsenal is stepping down, according to a statement issued on Saturday.
"It has been truly an honor and privilege to serve with you and to serve the country in the wide variety of roles and opportunities I have been presented," D'Agostino wrote in his farewell to the division.
His last day at NNSA will be Jan. 18, the final day of the Obama administration's first term in office.
Neile Miller, currently the principal deputy administrator at NNSA, will serve as acting administrator until the White House chooses a nominee to fill the position.
"Tom D’Agostino has proven himself to be a talented leader, a trusted adviser, and a true confidant," Energy Secretary David Chu said in a statement issued the same day.
"Under his watch, we have eliminated or secured hundreds of nuclear weapons worth of nuclear materials," Chu added. "We have reduced the number of deployed warheads to the lowest level since the 1950s . . . while successfully maintaining the safety, security, and effectiveness of a shrinking stockpile."
D'Agostino is the latest in a number of top U.S. national security officials to leave the White House as the administration enters its second term.
The White House filled one of those gaps on Friday, naming Sen. John Kerry (D-Mass.) to replace outgoing Secretary of State Hillary Clinton.
However, the Obama administration has yet to officially name its top picks for the Defense Department and CIA. Former Nebraska Republican Sen. Chuck Hagel has been tagged as the administration's presumptive pick for the Pentagon.