Last week's murder of nine black people in their place of sanctuary has confronted America once again with the specter of racism — past and present. One victim, Rev. Clementa Pinckney, who is lying in state in South Carolina's state capitol, will be eulogized Friday by the first black president. Meantime, there are calls for a "conversation" among white Americans — including both parties' candidates for the White House. But what about the future? Can the country move forward when we can't agree on the past?