A Gallup poll last week highlighted the sad but predicable racial divide in perceptions of the Martin case. Seventy-two percent of blacks felt that race was a factor in what transpired that night in February, while just 31 percent of non-blacks agreed with that sentiment. But to the extent that those numbers reflect something beyond a cause for pessimism, they show our different understanding of history. For many whites, the Martin case is a sad but isolated incident; for blacks, it is part of a matrix of suffering that stretches back to the days when black men were hung in public for sport. This is a divide between those who feel that the past is best left in the past and those who know that history is interred in the shallowest of graves.