Originally Posted by Steve Rupe

The Donald cannot personally fire Mueller directly. Only the Attorney General can fire Mueller directly. The Donald can order the AG to fire Mueller and if the AG refuses the Donald can personally fire the AG.

It is not in and of itself "obstruction of justice" for the Donald to order the AG to fire Mueller as he has the constitutional authority to do that.

The Donald can keep firing AG's until he finds one that will fire Mueller, the same as President Nixon did with the Special Prosecutor investigating him. The AG and the assistant AG would not fire the Special Prosecutor but the 3rd in line, Bork, did.