For supporters of Democratic presidential candidate Barack Obama it is a nightmare scenario -- his apparent lead in the battle for the White House suddenly evaporates on Election Day. The cause? Race. As Republican rival John McCain celebrates victory, it emerges that a small but decisive percentage of white voters who had declared to opinion pollsters they supported Obama actually chose differently in the privacy of the ballot booth. With opinion surveys making Obama the favorite over McCain less than three weeks before the November 4 election, attention has turned to the question of how many white Americans might be...