Barack Obama may or may not prove to be one of America's great presidents, but there is no doubt he will be one of the most written about. Stephen Sackur talks to David Remnick, the Pulitzer Prize-winning editor of the New Yorker magazine, and author of The Bridge, an acclaimed book about Obama's life and his rise to the presidency. For all the millions of words written about Obama, do we really know what makes America's first black president tick?