"Donald Trump is the first president in my lifetime who does not try to unite the American people--does not even pretend to try. Instead, he tries to divide us," Mattis writes. "We are witnessing the consequences of three years of this deliberate effort. We are witnessing the consequences of three years without mature leadership. We can unite without him, drawing on the strengths inherent in our civil society. This will not be easy, as the past few days have shown, but we owe it to our fellow citizens; to past generations that bled to defend our promise; and to our children."

He goes on to contrast the American ethos of unity with Nazi ideology. "Instructions given by the military departments to our troops before the Normandy invasion reminded soldiers that 'The Nazi slogan for destroying us ... was "Divide and Conquer." Our American answer is "In Union there is Strength."' We must summon that unity to surmount this crisis--confident that we are better than our politics."