Yes, this is the core of my own fear of what is happening, and why I have such short patience with those defending Sessions, or especially Mueller, for no good reason it seems. However, there are some good reasons why Trump hasn't fired Sessions YET.
First, the already mentioned reason that he is basically being blackmailed by guaranteed impeachment. But secondly, even though it is well within his authority, there are good hearted reasons why it is current tradition for the President to take a hands off approach with the DoJ, at least publicly. Not that I believe that was happening with Obama, but I do understand why it possibly should.
This could explain the berating of Sessions and the DoJ that Trump has apparently resorted to, or been reduced to, depending on your opinion. He is trying to make the case that he has been patient, to help provide him cover if/when he does lower the axe. He would have Grassley and Nunes and others arm in arm to show that it wasn't desired, but required, and other branches of government agreed.
In the meantime, he needs to be talking about these new Clinton investigations in the House and Senate, and use those as leverage on the DoJ, if he's not going to order the DoJ to do it himself. Otherwise, he'll continue to twist in the media wind, and suffer long term damage to his brand as you said while waiting for more pieces to perfectly line up before he pulls the trigger.
My guess is he knows this, and is not playing footsie with Mueller or playing games on his Twitter followers as some here seem to think, but is getting close to lowering the boom himself, if he has to.
However it occurs, it will definitely be fireworks time.