Rosenstein started this and has a duty to supervise it. If he recuses himself, Trump should fire him on the simple grounds that he is incapable of executing his duties as DAG.
Absolutely. Immediately. He really deserves to be fired now, for unnecessarily escalating the investigation to a criminal inquiry the way he did. In other articles I've read, Rosenstein apparently even told Mueller that he would be willing to recuse himself if Mueller decides he should, so apparently that is what we are waiting on, and proves Rosenstein isn't even supervising the case now.
Here’s one of the places it’s documented that Rosenstein told Mueller that he would leave it up to Mueller if Rosenstein should recuse himself. This apparently happened way back before Mueller was even appointed, which leads one to wonder if this all hasn’t been a setup from the start.
http://dailycaller.com/2017/06/04/russia-probe-may-expand-to-include-sessions-rosenstein/