There have been a couple interesting de facto postmortems of Bernie’s campaign about his failure to get or keep his most promising allies on board. First, with Elizabeth Warren:

Last weekend, a few days after Elizabeth Warren dropped out, Shakir and one of his deputy campaign managers, Ari Rabin-Havt, started contacting her top staffers and supporters to see what could be done to bring together the two camps before the primaries on Tuesday. Sanders spoke to Warren a “handful” of times throughout the week, a campaign aide confirmed, but she has declined to offer her endorsement. Several figures in Warren’s circle balked at the outreach effort — Sanders and his aides, they said, had months to lay the groundwork for that kind of partnership, but only did so this week from a position of desperation. About a month ago, when it was clear that Warren had little chance to win, one person inside the campaign said they put out feelers to Sanders’ operation in an attempt to create new lines of communication. At the time, senior Sanders officials showed little interest, the person said, in reciprocating.

Given how quickly the race changed and how recently Sanders had a reasonable expectation that he would be the nominee — Super Tuesday was less than 2 weeks ago — his lack of interest in working with Warren when first approached is at least somewhat understandable. But nonetheless is left him seeking her endorsement after it was no longer in her interest to give it if she wanted to maintain leverage over the Democratic nominee.

Perhaps more instructive are the campaign’s issues with Alexandria Ocasio-Cortez, whose endorsement helped him regain his leave over Warren. AOC pointedly defended Warren’s decision not to endorse Bernie here, and there’s some interesting background:

As Vanity Fair first reported in February, Shakir apparently communicated to Ocasio-Cortez his dissatisfaction over her remarks about alerting the presence of immigration authorities. While Sanders has sought to scrap and restructure the Immigration and Customs Enforcement agency in its current form, his campaign has been trying to avoid the impression that it was encouraging noncooperation with federal law as it exists, according to one source. (The Sanders campaign denied on Friday that Shakir ever spoke to Ocasio-Cortez about her immigration remarks.) After that, Ocasio-Cortez ― already annoyed with the campaign’s Jan. 23 decision to publicize the endorsement of controversial podcast host Joe Rogan ― grew less interested in helping Sanders’ campaign, according to the source. After her last event in Iowa on Jan. 26, she did not return to the trail for Sanders until 16 days later, at the New Hampshire rally featuring The Strokes.

On one level, of course, all of this is the 2020 equivalent of “Hillary shoulda campaigned in Wisconsin.” None of this was ultimately material to the outcome of the primaries; when you lose every country of a midwestern state you have to have getting a high-profile endorsement and some extra high-profile speaking appearances ain’t gonna do it. Still, even though it ultimately didn’t matter because she was drawing dead without at least one of Florida or Pennsylvania, Clinton’s failure to adequately focus on tipping point states could have mattered, and this is something Biden needs to take into account in 2020. So I think we can distill some lessons for the next progressive campaign for the Democratic nomination:

The “appearing on right-wing media venues is MASS POLITICS” argument is exactly as dumb as it appeared on its face. On the one hand, there’s no significant well of untapped voters waiting to be mobilized by social democratic policy proposals in these audiences, and on the other hand you run the risk of alienating allies who correctly revile these programs and outlets.

To win the Democratic nomination, you can’t run against the party. In particular, the party’s African-American base is quite ideologically heterogenous but very warm towards the party for obvious historical reasons. As Yglesias says, Bernie’s second disastrous performance in southern states wasn’t so much about a lack of effort as that running against the party rather than with it is just not going to work with either the ordinary voters or leaders you need to attract. Relentlessly focusing on attacking the “party establishment” is fine if you’re a protest candidate looking to influence the eventual nominee; if you actually want to win the nomination, you want Jim Clyburn working with you or at least not against you.

The theory that you can bypass attracting ordinary Democratic voters by attracting huge numbers of young voters and habitual non-voters has been pretty conclusively falsified. At a minimum, a strategy depending on it happening is extremely likely to fail.

Building alliances is a skill, and for all the weaknesses of his campaign it’s something Biden can do. He was able to get Harris’s endorsement because he didn’t overreact when Harris got her only traction during the campaign by coming close to calling him a racist in a national debate.

Again, a lot of this was unnecessary. Rank-and-file Democratic voters like Bernie! The problem was that too many senior members of his campaign don’t like rank-and-file Democrats. There’s no inherent reason a progressive campaign can’t appeal to them.