He has pulled the entire Dem party to the far left of the American political spectrum. Most of his followers don't have a clue what a Sanders Presidency would mean for the country.
"Four years ago, Sanders’ policy positions may have been considered far outside even the Democratic party mainstream. But today there is absolutely no daylight between him and Elizabeth Warren— even the Democratic “centrists” have lurched far to the left. Why should Democratic voters have to settle for the imitation (Warren) or Bernie-lite (Biden, Buttigieg, and Bloomberg), when they can have the real thing?"
https://humanevents.com/2020/02/04/bernie-sanders-will-be-the-democratic-nominee/