A suggestion for the restoration of progressive unity:

[BzaDem]

24. We live in a two party system.

Our Constitution is not compatible with more than two parties in practice. For the sake of democracy, there should not be strong barriers to running in a primary. I think demanding that candidates pledge to support the Democratic party is a reasonable requirement (and would not be reflexively be opposed to closed primaries, though I havent thought about it enough to have strong feelings). Such a requirement is reasonable because it is a pretty low bar. If you can't in good conscious identify as a member of the party, perhaps you shouldn't be running or voting in the primary.

But Sanders did so. He ran as a Democrat, pledged to support the Democrats in the election, and made good on the pledge. Any rule excluding Sanders would have to require some long time period of party membership prior to the election. That would be a hard bar to running (unlike a pledge, which one can freely choose to make). I don't think such hard bars are desirable or good for democracy, in a two party system like ours.

Note that I say all of this as an enthusiastic Hillary supporter in the primary and the general.