The Warren/Sanders nonaggression pact was a heroic effort inspired by a noble vision, but it contains a contradiction that could never be resolved. Regardless of all the other things Warren and Sanders agreed on, the fact that they were running against each other shows that Sanders thinks Sanders should be elected president, and Warren think Warren should be elected president. At some point, they were going to have to start giving reasons for supporting their respective positions on this issue. Those reasons were inevitably going to end up being aggressive, as their goal was to cause the nomination of one candidate and the defeat of the other.
Sanders was the first to break the pact, and he did it in what he (and/or his people) thought was the least aggressive way possible: by saying nothing about her policies, and criticizing only her electability. Warren objected to this, and responded in a somewhat passive/aggressive way by not describing a conversation with Sanders in the best possible light. There has been a lot of self-righteous finger-pointing since then, because each candidate’s followers think the other one broke the nonaggression pact. However, once we acknowledge that the pact had to be broken eventually, there is no legitimate reason to blame either of them for what they did. Neither of their behaviors would have been objectionable if they were just two candidates running against each other. We should acknowledge that that’s what they are, and always have been.
Up to now they have been working as a progressive tagteam, defending their shared vision against more centrist candidates. That was an effective strategy for thinning out the field, but the time for that strategy is past. Now is the time to stop focusing on their similarities, and start focusing on their differences, so that voters can make an informed choice. This can be done without slinging mud. Both candidates can explain how their positions differ and say, “This is where each of us stand. Vote for the candidate whom you thinks best represents your values and priorities. Both of us will honor the majority choice. Whoever gets the most votes will get the nomination, and the other one will take a cabinet post, so we can both work together towards our common goals.”