2016 Postmortem

Clinton lost the presidential election and Clinton bears responsibility for losing the presidential election.

Sanders lost the Democratic primary election and Sanders bears responsibility for losing the Democratic primary election.

By the rules of the games, both Sanders and Clinton lost, and both bear responsibility for their losses.

If the Democratic Party wants to lay out agreements that Democratic primary candidates can choose to or not too agree with in order to be considered legitimate from the perspective of the Democratic Party, then I think that those should be defined now and formally adopted by the DNC for application to the 2020 primary election. Those agreements could include how or how not one can criticize fellow primary contenders, etc.