With the economic crisis center stage, Barack Obama has solidified his lead, pulling ahead of John McCain by 10 points among likely voters, 53-43 percent, in a recent ABC News/Washington Post poll.
But the question remains: Is that margin enough?
"We've seen these types of leads disappear at election time," said Michael Dawson, professor of political science at the University of Chicago.
The concern is particularly at play for black candidates. It is called the "Bradley Effect," named after former Los Angeles Mayor Tom Bradley, an African American, when he ran for California governor in 1982. Some pre-election polls showed Bradley with a lead of 9 points or higher; but Bradley lost to Republican George Deukmejian by a little more than a point.
As the theory goes, people lied, saying they would vote for Bradley when they did not.