The dude in the video is paid staff, not a volunteer. That said, he is a very low level field coordinator so the campaign wouldn't have done high scrutiny, but there should have been at least a cursory check. He would also have had brief training and he reports up a chain of command that should have some idea of what he is saying.
I wouldn't make too much of the incident, BUT … there is always the reliable field test of "what if this had been a Republican staffer and campaign?"
Bernie should be asked to repudiate this at every stop from now until he leaves the race. And every other Democrat candidate should be grilled on it as well. That's what would happen if the shoe was on the other foot.
I wonder if Bernie has ever denounced the gulag? Or if he thinks Solzhenitsyn was a traitor to the revolution, and the Kolyma "reeducation" centers are on his bucket list for a second honeymoon.
Since it is happening WITHIN his campaign staff he needs to speak on it this week.