He was a 'traitor' who betrayed his country by selling military secrets to the enemy.
He 'turned traitor'. [=he became a traitor; he betrayed his country/friends]
She has been called a 'traitor' to the liberal party's cause.
(..) ( shouting ) Attack! ( shouts ) Fight, you cowards! ( growls ) You fucking traitor. The only traitors here are the ones who shoved their knives into their Lord Commander's heart. For thousands of years the Night's Watch (..)2016 TvShow: Game of Thrones Title: Home Season: 6 Episode 2