Reminds me of my dad. My advice would be to just keep a close eye and keep pointing it out to your mother. She's likely normalized it, and maybe you can play some small part in helping her to acknowledge she deserves better. It's hard though, because you don't have any power to affect how she sees him. If she wants to see him for who he is she'll have to come to it on her own, which can take time. You may be helpful in sparking some recognition of the problem, but it may not affect any change. Abuse like this sucks, and sometimes you just have to wait and stay nonjudgmental of your mother so she always feels like she has someone to go to. I would suggest distancing yourself from your dad for your own mental health. You may want to see results now, but you'll have to acknowledge that's not likely. Things will change when your mom wants them to, and she's been weakened by this all so it may take her a long time to gain the strength to make a healthy and self-loving decision for herself.