Bernie’s campaign has been taken over by a faction that believes US is comfortably numb and needs a jolt to wake up from its corporate stasis. As a result, when Bernie, the way to achieve their change through voting, failed. The believe that another 4 years of Trump, is the wake up call America needs, so someone like Bernie is voted in next time. Outside of it failing once in 2016, since Bernie did worse after 3 years of Trump, they believe this time it will work.
Edit: The problem being... Trump is farther away from Bernie on the authoritarian -> libertarian scale, than the wide economic one. Meaning, the major authoritarian changes by Trump, will make it more difficult to achieve economic goals in the future.