President Trump and Defense Secretary James Mattis at the White House in October. Mattis will be replaced by Deputy Defense Secretary Patrick Shanahan on Tuesday.
Chip Somodevilla/Getty Images
This photo taken from a U.S. military plane shows Chinese activity at Mischief Reef in the Spratly Islands in the South China Sea. China is building military facilities on disputed reefs and islands in the South China Sea.
Ritchie B. Tongo/AP
Secretary of State Rex Tillerson, with Secretary of Defense Jim Mattis, testifies during a Senate Foreign Relations Committee hearing on Congress's power to authorize the use of military force.
Manuel Balce Ceneta/AP
President Trump speaks with newly sworn-in White House chief of staff John Kelly at the White House on July 31. Kelly is one of four former generals who were appointed to top administration positions.
Jim Watson/AFP/Getty Images
Teddy Fischer and Jane Gormley, student journalists from Mercer Island High School near Seattle, wrote stories based on an exclusive interview with Defense Secretary James Mattis.
Courtesy of Charlie Fischer
President Trump and Defense Secretary James Mattis speak on Inauguration Day. Mattis travels to South Korea and Japan this week in the administration's first major foreign trip.
Pablo Martinez Monsivais/AP