I am not American, but I believe your first point to be incorrect. The AG is supposed to defend the constitution (including from the president). In her confirmation hearing in 2015, senator Jeff Sessions, who is to take her place asked her:

"Do you think the attorney general has a responsibility to say no to the president if he asks for something that's improper...?"

Ms Yates replied: "I believe the attorney general or the deputy attorney general has an obligation to follow the law and the constitution and to give their independent legal advice to the president."

She was confirmed 84-12 so it seems that they were happy with the response. I would also note that any lawyer who is tasked to defend you also has an obligation to inform the client of poor chance of success, in this case the AG not only thought the chance of success was poor but it was unconstitutional also.