The Bradley effect is a term to describe voter discrepancies, telling opinion pollsters they prefer a candidate and then voting for a different candidate on election day. The phrase came about after the 1982 California governors race in which Los Angeles Mayor Tom Bradley, an African-American Democrat, unexpectedly lost his candidacy for governor of California to candidate George Deukmejian, a white Republican, after pollsters were predicting Bradley's victory. The theory is that people do not want to appear racist, so they say they will vote for a minority candidate, even if they aren't planning on it.
2008 Democratic Primaries
In California and other states, Barack Obama was leading in the polls to Hillary Clinton. In California's primary, Obama lost by a landslide 10 percentage points after a late survey showed him ahead by 13 points. The Bradley effect was invoked.  Political scientist Bethany Albertson used data from 32 Democratic primaries this year. She found evidence of the Bradley Effect in three states, California, New Hampshire and Rhode Island.
2008 General Election
Liberal allegations that Americans are somehow racist were disproved by the 2008 general election results, as Obama did better than polls in many areas.