turn againstphrasal verb
Definition of turn against
1 : to stop supporting or being friendly to (someone or something) The senator eventually turned against the war. She turned against her best friend.
2 : to cause (someone) to stop being friendly toward (someone) He tried to turn our friends against us.
3 : to use (something) in a way that harms or discredits (someone) Her political opponent tried to turn her many years of experience in Washington against her.