I understand your point and I think your argument you are making has some merit, however you've moved the goalpost a bit here. Your original argument was:But Warren didn't endorse Sanders. Warren endorsed Biden.
She aligned herself with Sanders on many issues, but in the explicit context of a race in which they were not only competitors, and were widely perceived to be competing for the same votes. Her pitch was that she offered a similar suit of policy to Sanders, but without the obstacles I detailed. She reproduced and magnified the narrative that Sanders couldn't get elected and couldn't govern, and she did so for her own benefit. When she was finally asked to make a public commitment to the viability of Sanders' policies, of her policies, she refused, and waited until Sanders had left the race to endorse Biden as a "unity" candidate. Her ultimate role in the primary was to widen the perceived distance between Sanders and the party, which is precisely the opposite of what I'm describing.
andI'm suggesting that senior figures within the Democratic Party voicing their support for Sanders, privately and publicly, would improve his chances of securing the nomination.
So originally you were complaining that no Democrats voiced their support for Sanders. When I gave examples of that being incorrect, you've now changed that to complaining that Warren didn't "endorse" Sanders. Now of course another problem with this amendment of your argument is that it also ignores that AOC actually did endorse Sanders... but we can put that aside for a moment.If some leading Democrats, even just a small number, were to voice their support for Sanders, this would have challenged these assumptions. It would lend credence to the claim that Sanders was electable, and would demonstrate that the party was prepared to work with him.
"Voice support" which is what you originally argued, is different from "endorse". You know... or at least should realize, that by the time Warren dropped out, Sanders window for victory had closed. Even with Warren's endorsement, he still had no chance at a majority and thus no chance for the nomination. Warren realized this, which is precisely why she held back from endorsing him. She would have been committing political suicide for a lost cause. The fact that she waited until after Bernie dropped out just makes this all the more obvious.
What you seem to be trying to do here is essentially blame Warren for Bernie losing and cast Warren as being the one who alienated Bernie from the Democratic party and Democratic voters. But the reality, I would argue, is the opposite. If anything, Warren helped to highlight the mainstream nature of Bernie's policy proposals, and show that his positions were, in fact Democratic party positions. The polling about the overlap in Bernie and Warren voters showed clearly that although Bernie and Warren were drawing in part from the same progressive voter pool, many of Warren's supporters were not fans of Bernie and vice-versa. You've certainly heard enough Warren-hate from Bernie fans on this very forum, to know that Bernie voters and Warren voters are not 1 for 1 interchangeable... I know I have.
Warren started out her campaign with both arms wrapped around Bernie... using "I'm with Bernie" as her veritable mantra. But she was flat in the polls and taking criticism that she needed to distinguish herself from Bernie more. So she adopted the "I'm a progressive who gets things done" theme which you essentially reference and are claiming somehow undermined Bernie. I can see your point but jeez man isn't that the whole essence what campaigning for office is? How can she possibly run for office without drawing distinctions between herself and the people she is running against? Didn't her pitch always have to be "I'm like Bernie, but I'm better"? And since she and Bernie were the two "progressives" in the race, they could only co-exist by partly undermining each other, right? Just like all the "moderates" were "undermining" each other and diluting each other's poll numbers by their very presence in the race.
So in that sense, Bernie had just one candidate competing directly with him, while Biden had all the rest. In fact that was exactly what allowed Bernie to be in the lead for so long. His vote was less diluted than anyone else for longer than anyone else. Bernie only had one person to beat, while Biden had five... and Bernie still lost. That's not Warren's fault, or "the media's" fault or the DNC's fault. Its Bernie and Bernie's campaign's fault. What you seem to be implying here is that Warren and her voters had some sort of obligation to step aside and rally behind Bernie for the greater good or similar. Which is ironic, given how resistant a lot of Bernie voters are to the idea that they need to rally behind Biden.