I would add to the other explanation only that they both represent the progressive wing of the nation’s politics for their time, and are analogous to each other in that regard. Bernie is beloved and renowned for his civil rights activism and his incorruptible concern for regular folks and trying to make things better for people. https://en.wikipedia.org/wiki/Bernie_Sanders#Political_positions

Bernie “walks the walk” as they say, and has for his entire career.