whispering campaign
noun [ C usually singular ] disapproving uk/ˈwɪs.pə.rɪŋ kæmˌpeɪn/ us/ˈwɪs.pɚ.ɪŋ kæmˌpeɪn/
（破环他人名声的）造谣活动，散布流言蜚语的活动
the intentional damaging of an important person's reputation by saying unpleasant things about them that may not be true