My theory is Mueller is going to burn a Trump alley really bad so as to give the media and the left something to holdup as a victory. I do not think it will cause Trump any serious trouble but it will give the left something to claim as proof of their claims but maybe not the Russia claims. Mueller feels he must throw the left a bone even if the effects on Trump are superficial.
Mueller will vindicate just enough of the lefts claims to fuel them for the rest of the Trump presidency.