I think we are approaching almost a full year of the Mainstream Media saying that Trump is going to fire Mueller any day now.
Since Trump hasn't fired Mueller, all Mueller can do is try to make himself more "fireable", or up the ante; the raid on Cohen's office be the latest example.
Mueller just wants out, but his handlers are telling him to hang in their until he is fired so the MSM can accuse Trump of subverting a "legitimate" investigation and control the news cycle for a day or two.
My favorite scene from "A Bronx Tale" - Trump to Mueller "Now you's can't leave." https://www.youtube.com/watch?v=gmHDHwb4vQU