Secretary of Defense James Mattis greets U.S. Marine Corps Gen. Joseph Dunford, Chairman of the Joint Chiefs of Staff, after arriving at the Pentagon in Washington, D.C., Jan. 21, 2017. (DOD photo by Air Force Tech. Sgt. Brigitte N. Brantley)
On New Year's Eve, a short phone call will mark the end of Defense Secretary Jim Mattis' tenure and the beginning of Patrick Shanahan's command of the Pentagon.