How do you comfort your husband when your mother in law puts him down?

He is an amazing man, but nothing is ever good enough for her. He could solve all of the World's problems and she'd still call him a screw up.

And honestly? I hate her. She treats both of us like garbage and it takes all of my energy to not go off on her, ESPECIALLY when my husband, who NEVER cries, has to leave the room because she literally nearly drove him to tears with her words.

How do I comfort him without bashing her? How do I even begin to try to fix the damage she causes?