History supports me in this. In 1983, Harold Washington, a black man, was leading in the polls for Chicago's mayoral race by a wide margin but won with a much narrower margin. In 1989 Douglas Wilder, another black candidate, became Virginia's governor winning by less than a point although polls before the elections showed him leading by 9 points. In 1989 David Dinkins was leading by 18 points over Rudy Giuliani in New York's mayoral race but won by only 2 points. The most significant of all was Tom Bardley, a black dude, who was way ahead of his white opponent but lost the elections for governor of California.
History also can prove me wrong. These were all elections held in the 1980s. The country has changed since then, There are a lot of young voters this time. We also did not also see Obama suffering from any Bradley effect in the primaries, except probably in New Hampshire where he unexpectedly lost to Hilary Clinton. But if you look at the swing states like Ohio, Pennsylvania and Florida, there's a large population of people who may have a problem with Obama's race. Ralph Nader still has his supporters (3%) and he may take more of Obama's votes especially with Obama's opposition to gay marriage.
So what if Obama loses?
It would be only in electoral votes, just like Bush won in 2000 despite losing the popular vote. Politicians will seriously reconsider the electoral system.
Other than that, the country will be in shock. The only people who won't be shocked will be black people. Most of them have lost any confidence in the political system long time ago. This will probably kill any remaining hope that some of them still had in America, but a lot of them won't feel a thing (but I'm telling you, downtown LA will be wrecked). The people who will be in absolute shock are young people who are participating in this election. It will be sort of a wake-up call for them that tolerance exists less in US politics than it does in their college dormitories.
And then there will be the shock of electing another Republican, who voted with Bush 90% of the time, as the next president along with a vice president who has poor qualifications for any political office. The fact that Bush got away with all what he did was shocking enough, but the shock of electing a president for the incumbent party will be more shocking and disappointing to a lot of Americans.
I truly hope Obama will become the next president, but if he didn't that shouldn't come as a big surprise. It happened before and it will happen again.