'Hold fast': Mattis bids farewell to Pentagon

Defense Secretary Jim Mattis bade farewell to the Pentagon on Monday, telling the US military to "hold fast" after he quit over a series of fundamental differences with President Donald Trump.Mattis resigned December 20, after Trump stunned the US establishment by ordering a full troop withdrawal from Syria."Our department is proven to be at its best when the times are most difficult," Mattis said in a brief memo to the Pentagon, an apparent reference to the turmoil in Washington.