Had 100% of Sanders supporters shown up to support Clinton as opposed to the 80% that did, while 20% sat on their asses pouting or, worse, turned out for Trump just to spite "neolibs" or stir the pot for "change", the Progressive agenda would have been four years farther along under a Clinton administration, and very likely far fewer Americans would be dying too.
Even Sanders understands this.
Progressives, admirably, stand for the "greater good" but in this case only the blind cannot see that the greater good is laying waste to Trump and his congressional enablers at the ballot box by whatever means necessary. If they can't get behind this, they and their agenda deserve to be marginalized, rather than incorporated.
Thankfully, in America, in the real world where I live among Progressives and folks of all types of political persuasions, most have come to the same conclusion. Even my 14 year-old daughter gets it. The only folks running down Biden that I know are Trump cult members.