Living history, and knowing that you're living history, creates a real burden of responsibility: on the leaders shaping that history, on those seeking to understand it, and on every day citizens trying to decide what to do next.

We take stock of this moment with David Gergen, who has advised four U.S. presidents: Nixon, Ford, Reagan and Clinton. He's also the founding director of the Center for Public Leadership at the Harvard Kennedy School, where he is a professor.