Conditions in 2020 were as ripe as they ever could be for an incursion into the party... There was never, and will never be a better time to strike.
Consider:
Material conditions will continue to deteriorate for vast swaths of the population.
The mainstream acceptability of socialism (or at least New Deal-scale approaches to problems like healthcare, education, and climate change) will continue to increase.
Bernie, for as good of a candidate as he was, still has a number of significant flaws. He's an old white guy from a tiny state who is honest but not particularly charismatic, he had to create a whole left-ish movement from scratch, and he had a health scare in the middle of a campaign.
It's not hard to imagine a scenario where people are worse off than they are today, where socialism is more popular than it is today, and where there's a better candidate on the left wing of the party.
Consider:
It's not hard to imagine a scenario where people are worse off than they are today, where socialism is more popular than it is today, and where there's a better candidate on the left wing of the party.