Donald Trump’s pick for Secretary of Defense is an outspoken former Marine Corps general known as “Mad Dog,” but don’t let the name fool you. James Nicholas Mattis is an insightful, charismatic leader whose motivational abilities and battlefield successes came with nuanced understanding of history, humanity and his enemy. Also called “the Warrior Monk,” the well-read native of Pullman, Wash., joined the Marines at 19 and retired three years ago after heading Central Command, where he oversaw wars in Iraq and Afghanistan and conflicts in Syria and Yemen. There were signs even before early December’s announcement that the 66-year-old, who’s never owned a television, never been married and has no children, was influencing the president-elect on key policy issues. Trump told The New York ...