Ken Burns Still Has Faith in a Shared American Story By David Marchese It cannot be said that Ken Burns is an unambitious filmmaker. He is, after all, a director who has spent 40 years making documentaries about truly foundational American subjects: the Civil War, Thomas Jefferson, jazz, the Roosevelts, baseball, the Brooklyn Bridge, the Vietnam War, country music. The list goes on. (And on. Think of an iconic American historical figure or event, and there’s a half-decent chance that Burns, 67, has made or is currently making a documentary about it.) But Burns’s greatest audacity might simply be his belief that the stories he tells about those biggies and their attendant ambiguities, hopes and disappointments can resonate with all Americans, across political or ideological divides. “It’s important for me to speak to everybody,” says Burns, whose documentary about another biggie, “Hemingway” (directed with Lynn Novick), premieres April 5 on PBS,