Sessions quite properly recused himself. There are a lot of legal columns talking about it - and the DOJ guidelines (posted here many times) were quite explicit.
Mueller should also be recused. He has way too many conflicts of interest to have ever been considered - irrespective of what idiot Ryan has to say about him.

Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...