The job of the Attorney General is to enforce the law. Period. Not to run interference and be a spineless yes man for a president who sees himself as a king and demands unquestioning fealty from his subordinates.
This is why Trump is such an abysmal president -- he has not one clue regarding how our government works, and shows no interest at all in educating himself on it. Trump went in believing that "president" was the same thing as "king" or "dictator." He thinks he can just point and say "This is what I want and that's how it's going to be." But that's not how the United States rolls. Our government is built on a system of checks and balances designed to prevent absolute power from falling into the hands of a single individual. As president, Trump has a lot of power. But he doesn't come even close to having ALL of it.
Attorney General is a principal government position; a principal position is one that answers to no one but the president himself. All principal government positions require Senate approval. Trump wants to completely bypass Senate approval and plug in his choice, Matt Whitaker -- a partisan Republican and Trump supporter who is already on record has having asserted a preconceived and biased opinion against the Mueller investigation.
It's not going to happen.
Trump wants Whitaker because he thinks Whitaker will do what Trump says and shut down the Mueller investigation. There's a hitch, though. You know how during jury selection, they instantly rule out anyone who has already formed a specific opinion about the case in question? Same thing applies in regards to Whitaker's preconceived anti-Mueller opinion. If the Senate does approve of Whitaker, and he is appointed as the new AG, he will have no choice but to recuse himself from overseeing the Mueller investigation because of that opinion, which is a matter of record.
So no. The AG's job is not to follow the president's orders. His job is to enforce the letter of the law -- objectively, zealously and without personal bias.