Personal credibility may be destroyed or undermined for many reasons such as that the person undermined may be a political, business or social opponent whilst by the same token the accusing person or party may thus have increased their status.
For instance, in the USA the new Republican Party Speaker of the House's personal attacks against the then Democratic Party Speaker of the House over his book deal forced his resignation in 1989 as Speaker of the House, yet the new Republica Speaker has recently signed a book deal himself.