Brazile on leaking debate questions[1]:
>My job was to make all our Democratic candidates look good, and I worked closely with both campaigns to make that happen.
Tad Devine, senior aid to Bernie's campaign on the debate questions leak[2]:
>She would get in touch all the time for guidance, so I can verify her recollection on this issue
So the question of whether the leak was "unfair to Bernie" is not established. The fact that Bernie never responded critically of the leak suggests Brazile's actions weren't unusual for either side. But this just underscores the fact that a lack of context and selective leaking allows one to present a false narrative.
>Destabilizing - the Hillary campaign promoted Trump as a candidate.
Promoting Trump was certainly a miscalculation. But it was not at all "destabilizing" in the sense the OP meant.
[1] https://time.com/4705515/donna-brazile-russia-emails-clinton...
[2] https://www.chicagotribune.com/nation-world/la-na-trailguide...