There is a zero percent chance that Bernie endorses Joe if he drops out. He played ball with Hillary and the DNC in 2016, and they’ve still been trying to fuck him this time around. What does he have to lose in that scenario? Continuing to NOT get their support? Fuck it, he can do what he wants at that point. No amount of grandstanding is gonna make ANYONE who doesn’t already support Biden get excited about his candidacy.
At the end of the day, Biden wants exactly the same thing as bernie, he just wants to accomplish them with more moderate(and imo rational) means. I'm sure he sees this and I'm sure he realizes that some progress(Biden) is better than no progress(trump).
Its not about being excited about Biden, its about defeating Trump and the GOP.
Grandpa Joe says " We can reelect Donald Trump !"