The once unthinkable could happen this November: A black man may win the presidency. When freshman Illinois Sen. Barack Obama was born in 1961, African-Americans couldn't vote in parts of the United States. Now, as Obama prepares to accept the Democratic nomination in August, he is running slightly ahead of his presumptive Republican opponent, Arizona Sen. John McCain, a 71-year-old Vietnam War hero. First dogged by questions of whether he was "black enough," Obama now faces doubts about whether racial prejudice will prove a major obstacle to his historic campaign, especially among white working-class voters. Nonetheless, Obama is likely to benefit from changes in the country's demographic makeup, which is growing less white as immigration diversifies. At the same time, younger voters are showing notably less racial prejudice than older generations. Meanwhile, some top Republicans acknowledge the GOP needs to appeal to a broader range of voters if McCain is to win.