Is criticizing public officials, their policies, and their decisions considered backbiting (gheebah), and how can one rid themselves of backbiting?

The criterion for backbiting is your mentioning of your brother with what he dislikes. This includes speaking about and criticizing a public official with what he dislikes, unless it is for seeking redress and there is hope of removing injustice, or if the person is openly neglecting the rights of the people. However, if the criticism and speech are without a legitimate Sharia (definition) interest, then it is either backbiting if it is true about him, or slander if it is not true about him.