Comedy is serving a ten year term. In his words, you’re stuck with me. He would have to be found in gross violation of his office and it would still be hard to get rid of him.
It is a 10 year term but the President can fire the Dir/FBI if the President has “.. lost confidence in the Dir/FBI’s ability to do the job ..”.
So why doesn’t Trump fire him? I have no idea!
Maybe waiting for the whole “Russian-interference-the-election “thing to die so Trump can’t be accused of killing an “investigation” for political reasons.