IDIOMS

whisper campaign

(idiomatic) A method of persuasion in which damaging rumors or innuendo are deliberately spread concerning a person or other target, while the source of the rumors tries to avoid detection.

Example: 1920, "Harding Ignores ‘’Whisper’ Campaign," New York Times, 1 Nov., p. 1 (retrieved 17 Aug. 2009):
  Senator Harding will not authorize his headquarters to take public notice of the “whispering campaign.” There has been a difference of opinion among his advisers as to whether to ignore the slanders or to produce evidence disproving them.
1976, Donald Horne, "The campaign of the media," The Age (Australia), 12 Feb., p. 8 (retrieved 17 Aug. 2009):
  Both publicly and in a particularly unscrupulous whisper campaign the Liberals tried to change the aspect from one of folly to one of personal corruption and some of this got through to the voters.
2008, Ana Marie Cox, "S.C. Takes a Chance on McCain," Time, 20 Jan.:
  McCain—who was famously burned in South Carolina in 2000 after his New Hampshire victory, when a whisper campaign and George Bush's dominance of the state's Republican party structure combined to deliver a crushing blow—was openly nervous.