That's not hw this works. This is about rival groups in the party fighting over who get to lead it, and the left is really bad at winning in that arena. Biden got within spitting distance of winning the presidency right now and won the nomination, thats more than Bernie can say. There's this strange meme going around that just because Biden and the centrists don't dominate everything the left would clean up. If the latter were true the positions would be reversed in reality. It's magical thinking, not based on fact.
If Biden candidate can't do this, no way would a leftist candidate do this. The don't get too inherent Biden's strengths, they have their own weaknesses. People were outraged at Biden being a "socialist" think how worse it would be if that were not only true but they were on tape signal boosting Fidel Castro more than once in 2019. Many have tried, instead the end up getting burnt.I think Biden ran too much on not being Trump and if people want to bring up his progress agenda (that there is was no guarantee he was going to implement if he won), it's dead in the water because the Dems could not move the needle on the Senate. The Clinton ''Third-wave'' machine is a failure, break it, burn it and then bury it, it belongs back in 1992.