When Dennis Kucinich was running for president, the threshold to participate in the debates was 2 or 3 % National polling. When he reached it, The Democratic party changed the rules to 5%. Every time Dennis reached the threshold it was raised.
DNC Chair Debbie Wasserman Schultz on MSNBC last night didn't say what the rules for the 2016 debate stage would be, only that there "would be a threshold." Since Bernie would probably poll a little higher than most, we should probably watch the maneuvering, maybe around endorsements or some other measure.
It may fall on us to be sure that progressives are allowed to have Bernie as our voice at the debates.