Campaigning for president in 1980, Ronald Reagan told stories of Cadillac-driving "welfare queens" and "strapping young bucks" buying T-bone steaks with food stamps. In trumpeting these tales of welfare run amok, Reagan never needed to mention race, because he was blowing a dog whistle: sending a message about racial minorities inaudible on one level, but clearly heard on another. In doing so, he tapped into a long political tradition that started with George Wallace and Richard Nixon, and is more relevant than ever in the age of the Tea Party and the first black president. In Dog Whistle...