For example, part of the unfortunate history of American has been racsim toward blacks and even today some voters still might harbor racist attitudes. Part of that rascism was to deny recocnizing black men as men and instead call them "boys." An example of a dog whistle would be in a Presidential debate, refering to everone as "Mr. (LASTNAME)" but if there's a black candidate or moderator, he and only he is reffered to by his first name. Racists in the TV audience then get a veiled message to vote for the candiadte who calls black men by the first names. Just one example. In fairness, I do not personally think candidates who do this are themselves racist but rather are simply trying to get as many votes as possible, essentially using voters' own bigotry against them. It does however speak to the culture of the political party that has the support of people who identify with tactics like this being used.