Smear Campaign

A smear campaign, smear tactic or simply smear is a metaphor for activity that can harm an individual or group's reputation by conflation with a stigmatized group. Sometimes smear is used more generally to include any reputation-damaging activity, including such colloquialisms as mud slinging.

Common targets are public officials, politicians, and political candidates. Smear campaigns are often based on information gleaned from opposition research conducted by paid political consultants. To a lesser degree, the term can refer to an attempt to damage a private person's reputation; for example, during a trial, the opposing counsel may attempt to cast doubt on the reliability of a witness.

Fifth Book
In the fifth book, Harry Potter and the Order of the Phoenix, the Ministry of Magic has been waging a smear campaign against Harry and Dumbledore, disputing their claims that Voldemort has returned. A new character is introduced when the Ministry of Magic appoints Dolores Umbridge as the latest Hogwarts' Defence Against the Dark Arts instructor (and Ministry spy). Because the paranoid Ministry suspects that Dumbledore is building a wizard army to overthrow them, Umbridge refuses to teach students real defensive magic. She gradually gains more power, eventually ousting Dumbledore and seizing control of the school. As a result, Harry's increasingly angry and erratic behaviour nearly estranges him from Ron and Hermione.