Secretary of State John Kerry at the Agency for International Development on Friday. (Michael Reynolds/EPA)

Another longtime aide to Secretary of State John F. Kerry is taking a senior post at the State Department. David McKean is to be director of policy planning, a plum position created in 1947 by George F. Kennan and held in later years by foreign policy heavy hitters such as Paul H. Nitze, Mort Halperin and Richard N. Haass.

McKean became the Senate Foreign Relations Committee’s staff director when Kerry took over the committee in 2009 and was his Senate office chief of staff from 1999 to 2008. He left the committee in early 2011.

McKean was also CEO of the John F. Kennedy Library Foundation in Boston and has written three books on U.S. political history.

Last April, McKean become a senior adviser to then-Secretary of State Hillary Rodham Clinton for the Quadrennial Diplomacy and Development Review, assessing State Department operations. Ought to come in handy as Kerry takes over. And his long relationship with Kerry should enable him to provide candid advice — a valuable commodity in this town.