"Mr. Grav...Grindelwald says that Credence has helped free all the wizards and witches. He tells him that they're helping the people without magic, too. So why do so many people look at him with horror and revulsion?"

Before Grindelwald can hit him or reject him, Credence manages to get out that he was the one that killed his mother and sister. Because of this, Grindelwald maintains their relationship and, with Credence's help, takes over America.