The Attorney General represents in the United States of America. Not individual cabinet officials. Not the president. This refusal to do his job is grounds for his own impeachment. 
BASH: Do you see it as your job as attorney general to represent anyone in the administration being investigated by Congress? BLANCHE: Wait, do I see it as my job? The Constitution sees it as my job! BASH: So if Hegseth faces impeachment, would you represent him? BLANCHE: Well, yeah