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.
(..) he had disagreements. - I mean, with government policy. - GRANDPA: One hears of such men. Disturbed, most of them, or just plain cowards. FATHER: Even so, all of them traitors. GRANDPA: Absolutely right. Presumably, if that was the case with your father, you will have informed your superiors, (..)2008 The Boy in the Striped Pajamas