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.
(..) Enemies to the south... Ellaria Sand and her brood of bitches. Enemies to the west... Olenna, the old cunt. Another traitor. Enemies to the north. Ned Stark's bastard has been named King in the North and that murdering whore Sansa stands beside him. (..)2017 TvShow: Game of Thrones Title: Dragonstone Season: 7 Episode 1