text: Q amp;A David Gergen, political analyst, on leadership David Gergen , director of the Center for Public Leadership at the John F. Kennedy School of Government , was an adviser to four US presidents: Nixon, Ford, Reagan and Clinton. He is editor-at-large at U.S. News  amp; World Report and a political analyst. Gergen, whose center helps develop future leaders, talked to Boston Globe staff reporter Diane E. Lewis ...