He did. And he was wise to keep Sessions on as long as he did. I forget who said it, but in the report one of President Trumps advisers warned him of re-creating the Saturday Night Massacre.
Firing Mueller or Sessions or Rosenstein in an attempt to stop the witchhunt would have been the worst disaster Trump could have made.
B’rer Mueller was trying to get fired. “Throw me in that briar patch.”