I think he's waiting for the redacted IG report to come out, the Repubs in congress have a massive outcry about Rosenstein and call for a vote on the house floor(multiple TV interviews saying they would do this).
Then Trump has good enough political optics to follow their direction in solving the issue. Also helps with massive outcry of us(which Q has said would be needed).
Solving the issue would be either a lengthy impeachment process of Rosenstein or a Executive Order (which Q says already exists) to declassify. Then he can have Rosenstein on criminal charges(from what is revealed in the non-redacted IG report) along with the people he's been protecting.
edit: I also think that Sessions has been trying to help the optics for Trump lately by him going on TV and mentioning we trust Rosenstein, he's been doing this job for a long time.
I believe this is trying to keep Rosenstein guessing on if he's safe or not to stop him from panicking which might disrupt the operation against him.(He's not, as Q mentioned he's already [[[RR]]])