un·der·mine 
/ˌʌndɚˈmaɪn/ verb
un·der·mines; un·der·mined; un·der·min·ing /ˌʌndɚˈmaɪn/ verb [+ obj] : to make (someone or something) weaker or less effective usually in a secret or gradual way
▪ She tried to undermine my authority by complaining about me to my boss. ▪ The events of the past year have undermined people's confidence in the government.
▪ She tried to undermine my authority by complaining about me to my boss. ▪ The events of the past year have undermined people's confidence in the government.
