вести борьбу медленными темпами(Police have been nibbling (away) at crime in the city for years. [=police have been very slowly reducing the amount of crime in the city] VLZ_58)
придираться(Reviewers have nibbled at phrases, but have avoided the principal questions. – Критики придирались к выражениям, но избегали обсуждения главных вопросов. VLZ_58)