Again with the Bernie victim narrative. This has so little to do with shady "Democratic establishment" machinations and so much to do with straight and regular politics. Sen. Sanders was always an outsider insurgent candidate and was fortunate to get a hearing in the primaries of '16 and '20 at all. Very few political parties would have allowed a non member to contend for this nomination, and the VOTERS of the Democratic Party rejected him roundly in '20. He had the most money, the deepest organization across the states, the most fervent supporters...he just didn't have the product. Nevada was an obvious outlier, at least it should have been obvious to his supporters. Nevada, as a caucus state, was teed up for his type of run, but he could never parlay a less than majority win into momentum.

You are entirely right, "the left" needs to build strength to be taken seriously. If they can keep young voters engaged in politics, if they can refrain from convincing them that the "system is rigged" and thus not worth their attention, then time is on their side.