Please answer the question. Leaks may also be from disgruntled staffers whose idealism shattered on encountering the hard realities of American political system.
Also, there's been some claims that NSA and other agencies are running TOR exit nodes. Not sure if there's anything to it, but the point is state level actors have resources that nobody else does.
Besides, I am not sure what is your point. "Russian hackers would have covered their tracks, therefore it must not have been Russian hackers"?