It goes back before Donald was in charge of the Trump real estate business. It started with a really really shitty father who desired a “killer” business instinct in his children (read: cruelty) above all else.
Reading some of Mary Trump’s books will give some insight on the family that Donald grew up in. No love, all cruelty.
Donald is just a rich kid who inherited a big business and learned nothing but cruelty from his daddy.