The Bradley Effect

To those of you who propose the hideously false notion that I must be a racist because I wonder whether Dr. Ben Carson is polling better than he will eventually perform at the ballot box, it is because it has happened before. 
Please read the following excerpt from Wikepedia:

"The Bradley effect (less commonly the ((Governor Douglas)) Wilder ((or Mayor David Dinkins)) effect) is a theory concerning observed discrepancies between voter opinion polls and election outcomes in some United States government elections where a white candidate and a non-white candidate run against each other.
"The theory proposes that some voters who intend to vote for the white candidate would nonetheless tell pollsters that they are undecided or likely to vote for the non-white candidate. 
"It was named after Los Angeles Mayor Tom Bradley, an African-American who lost the 1982 California governor's race despite being ahead in voter polls going into the elections."