An alienating parent usually shows narcissistic and also borderline tendencies.
Narcissism is selfishness on steroids. Narcissistic individuals tend to be self-absorbed. Most centrally, they show deficits in ability to listen to others’ differing perspectives. Instead they hyper-focus on what they themselves want, think, feel and believe without taking into consideration others’ desires and ideas.
A narcissistic alienating parent uses the children as weapons, pawns in his/her battle to destroy the other parent. They claim to be protecting the children against the evil other. In fact, by using the children in their perpetual fight to hurt the other parent, they show little capacity for taking into consideration what is in the best interests of the child.