tarnish
verb uk/ˈtɑː.nɪʃ/ us/ˈtɑːr.nɪʃ/
(METAL)
[ I or T ]（使）（尤指金属）失去光泽，（使）变暗淡;（使）褪色
to make or (especially of metal) become less bright or a different colour
(GOOD OPINION)
[ T ]诽谤;中伤
to make people think that someone or something is less good
By this time a series of scandals had severely tarnished the candidate's image/reputation. 到这时，一连串的丑闻已使这名候选人的形象／名誉大大受损。