ˈwhispering camˌpaign noun [countable] a situation in which someone privately spreads criticism about another person in order to make people have a bad opinion of them
[TahlilGaran] Dictionary of Contemporary English ▲
whispering campaign n. The spreading of false rumors, or saying bad things, about a person or group, especially in politics or public life.
A bad man has started a whispering campaign against the mayor, saying that he isn't honest. [TahlilGaran] English Idioms Dictionary ▲