In his 33-year career as an American diplomat, Ambassador William J. Burns served his country through good times and bad. From the gilded halls of Putin’s Russia, to secret nuclear talks with Iran, to his seat in the Situation Room during the Navy SEALs raid that killed Osama bin Laden, Burns has played a role in some of the most crucial diplomatic episodes of our time. Now, as president of the Carnegie Endowment for International Peace, he’s fixing his gaze on the future. In “The Back Channel: A Memoir of American Diplomacy and the Case for its Renewal,” Burns maps a path for American leadership in the face of a changing world order and explains why now, more than ever, diplomacy should always be “our tool of first resort.”