There will be lots of post mortems on the mistakes Sanders’ campaign made. They’ll all be right. His campaign made plenty of mistakes.
But bottom line: Sanders doomed his campaign before it launched.

Now let’s be clear. Sanders entered 2020 with huge advantages over every other candidate. MORE advantages than Hillary had in 2016 which Sanders considered rigging the primary in her favor. Yet he and his team blew it. https://twitter.com/oldladydem/status/1221234172104257536

Sanders predicted, correctly, that if he ran his same 2016 campaign, he’d get 30% of the vote. A competent candidate would’ve strategized “how do I grow that to >50%?” Instead, Sanders, unwilling or unable to grow, asked “how can I win with 30%?”

Never one to let reality get in the way, Sanders and his insular circle hatched a fantasy scenario where he could win with 30%. All it required was an unprecedented 4 or 5 candidates arriving at the convention with delegates split in such a way that Sanders’ 30% was a plurality.

Implicit in his 30% strategy was a decision to ignore anyone outside his 2016 base, most notably black voters. That shouldn’t be surprising. Sanders has never been interested in developing relationships with black Dems and his attempts to do so ahead of 2020 were feeble at best.

Example of his “outreach”: Weaver met with members of the CBC to arrange a “get-acquainted” dinner for Sanders with one of them. Members of the CBC are his colleagues and after 29 years serving alongside them, he doesn’t have a personal relationship with a single one.

Aside: How tf does BS, or those who support him, believe he’s suited to be prez when he so clearly loathes building relationships outside his inner circle. He'd succeed on the world stage? GTFOH. There’s good reason only 11 members of Congress backed him in 2016, only 10 in 2020.

Back to his 30% strategy: Rejecting advice from experts on how to win the nom, Sanders believed running a grievance-driven “us vs them” campaign demonizing the 70% was the best way to appeal to the 30%. So that’s what he did. In his stump speech, in his emails. Consistently.

He hired staff & enlisted surrogates who refused to back our 2016 nominee and who he knew wld alienate the 70%. What better way to win the nom than to have senior staff entertain your 30% by trolling Dems (including random strangers) on Twitter & employ childish antics, amirite?

Adding to problems executing his 30% strategy, Sanders supporters … and Russia … didn’t get the memo that Sanders needed other candidates to stay in the race and did everything in their power to hurt those candidates and make them nonviable. https://twitter.com/oldladydem/status/1221238126196207621

Sanders’ staff, surrogates, and allied orgs did the same. Hell, Sanders himself undermined his 30% strategy by going to MA and MN in an effort to win those states and embarrass Warren and Klobuchar into dropping out.

Then when polling showed those candidates had no path and they dropped out, Sanders’ pollster, the same pollster who told him he was w/in inches of Biden in SC, called a common occurrence throughout primary history “unprecedented” and BS ran with that as his excuse for losing.

Nonetheless, even if that ludicrous part of his fantasy had come true, if 4 or 5 viable candidates stayed in until the convention, the sheer stupidity of his 30% strategy was demonstrated on Super Tuesday, on every following primary day, and in every poll.

The 70% he demonized were never going to move into his camp. Not during the primary and not at the convention. His fantasy of bringing the 70% to heel at an ugly, divisive convention was never going to happen. Dems would never give the nom to someone soundly rejected by our base.