As a numbers guy, not really ideological, I'm fascinated about this group of progressives, Sanders supporters. It's hard to put a percentage on what percent of the democratic party these folks make up. Looking at the available numbers to include primary votes and other polls which do break down ideology, I'd say progressives make up somewhere from a quarter to a third of the Democratic Party. Yet they seem to think they who make up a quarter to a third should have the say in who the democrats nominate and exactly what the democratic party's ideology should be without regard to the other 2/3rds to 3/4ths.
I've never been an ideologue, so a lot of this leaves me scratching my head. This isn't to say I don't respect who Sanders supporters will vote for or if they choose not to vote at all. That's their decision and we all have our own reason why we vote the way we do or don't vote at all. Reasons that make perfect sense to them even though others may look on their reasons as being asinine.
I'll add this which may help to explain it. Looking at the exit polls from the primaries it's easy to see Sanders received the big majority of independents who voted in the Democratic primaries. Biden had the support of a huge majority of those who identified themselves as Democrats. Sanders labels himself a independent, not a democrat. So even if I was a left leaning independent, a independent that leans toward the Democratic Party, I wouldn't have the loyalty to the democratic party that those who affiliate or identify themselves as Democrats. Even thought I lean toward the democrats, my vote is still up for grabs. Although I will choose to vote democratic 3 out of 4 times. Historical average. I'm not a party faithful or loyalist which votes for the democratic party's candidates 90% plus of the time regardless of who that candidate is.
To lump all Sanders supporters as Democrats is wrong. I'd say at least half or perhaps a bit more are independents, not party loyalist. the polls, exit polls, favorable/unfavorable polls, even head to head matchup's show this.
It's high past time that we start electing Americans to congress and the presidency who put America first instead of their political party. For way too long we have been electing Republicans and Democrats who happen to be Americans instead of Americans who happen to be Republicans and Democrats.