It seems that Mueller and most of his staff should have recused themselves because of conflicts of interest. But only Jefferson Beauregard Sessions III did so.
Spit.
Many believe that Sessions was double crossed by Rosenstein, who was the key player in getting Comey fired (as Comey worked directly for him) and the subsequent appointment of Mueller.
Did Rosenstein pressure Sessions to recuse himself from Russia probe to ultimately get Mueller appointed Special Counsel?
http://netrightdaily.com/2017/12/did-rosenstein-pressure-sessions-to-recuse-himself/