Occam’s Razor: Trump is satisfied with the job Rosenstein is doing. He’s not the one complaining. Trump can have that information released by making a phone call. Congress is the one doing the yelping.
For those who keep insisting “obstruction!” is why Trump won’t fire Rosenstein or Sessions- those two are administrators, they aren’t running investigations. The 1926 SCOTUS decision Myers v United States gives presidents the unrestricted authority to fire executive branch officials. Congress can’t impeach him for exercising a power that is solely his.
Occam’s Razor: Says Rosenstein will hang himself. No need for any outside help.