I’ve posted at #89 how Sessions came to recuse, but you might have better insights than I.
I take your point that the Ethics Office could have been staffed with liberals who had a different agenda. Of course, I doubt they could have foreseen the firing of Comey, which led to the appointment of a special counsel. I would like to know how Rosenstein was selected as his deputy. If there was a major mistake, his appointment was it. Rosenstein was confirmed 94-6.