The Pres. has a very narrow window of time, when he can fire them all, because it's only "all over" for now and will start anew like Freddy Krueger in a few weeks. Once a new witch hunt is underway, POTUS would be charged with interfering, obstruction of justice, etc., if he fired anyone. Same goes for investigating Bidens or Burisma or any Dem politicians on the take.
This is a very good point!
And ammo for the (D)'s to launch another "impeachment."