I'm not sure what your point here is but I see several possibilities:

  * Is independently supporting Sanders' campaign, maybe even volunteering.
  * Is gainfully employed by a pro-Sanders PAC.
  * Is gainfully employed by a something other than a PAC that is pro-Sanders.
  * Is gainfully employed directly by the Sanders campaign.
  * Something else

It isn't clear to me which of those is the case, but I assume it's the first. If he's actually employed by Sanders, that'd make his post a pretty odd thing to do. I think there are a lot better ways to have dealt with it (actually, I guess that's true either way).