Bernie Sanders’ formula for winning the election was base mobilization–nothing else. As one of his young followers put it memorably on Twitter, “There are no @#@#@ swing voters!” He made no effort to accommodate centrists, or even to package his opinions in a way that was more palatable to them. The results speak for themselves.
Donald Trump operates in the same way, and with the same electoral model. He has done nothing but feed his base red meat for 3+ years, presumably because he thinks they represent a majority of the country. He believes they alone won him the 2016 election. He’s wrong, and the polls prove it.
If Biden wins, will everyone wake up and realize that there are, in fact, swing voters, and that you still need to move to the center to win national elections in this country? The center left already understands that. It’s doubtful the right does.