By hiring investigators and lawyers who would stretch and even break the usual norms of investigation and charging. Compared with Comey going soft on Hillary's email, just to compare.
If Trump wants the most convincing "clean bill," he hires an adversary to do the digging, not a friend.
I see, but by “going hard” what do you mean, exactly? What they’ve been doing? Because there is no way that Mueller will actually come up with anything when the “investigation” is all finished.