It's a terrible Catch-22 for them because they'll alienate Bernie supporters and just like in 2016, they won't come out to vote because they'll feel disenfranchised. Who wouldn't, the primary is rigged and now the DNC is attempting to steer everyone to Biden just as they did Hillary.
It wasn't long ago when it appeared Biden might be out of the race but out of nowhere his support began skyrocketing. Why? What has changed? Immense fear that Trump will have an easy win in 2020 if Sanders is nominated. Even Biden is questionable but what can they do as no other candidate has a chance against Trump.
I don't like Sanders but I feel sorry for him and his supporters because the people he's competing against have the referees in their pockets.