So, if Biden jumps in who will his votes come from?
There's not much difference between him and Hillary ideologically and they have comparable political resumes. Biden's is officially longer, but Hilary has SoS and advising Bill.
Biden is more "common man" while Hilary is more patrician.
Biden, so far, doesn't have the scandals that Hilary does.
Some will vote for Biden because he's not a woman while some will vote for Hilary because she is one.
Biden has a somewhat deserved, somewhat undeserved goofy and loose cannon reputation.
Then, there is Sanders. How many support him because they're true believers and how many because he's not Hilary? If his support is mostly ideological, he gains by Biden's entry. If his support is mostly anti-Hilary, he loses by Biden's entry.
I don't know.
I'll keep supporting Sanders until another actual progressive looks viable . . . or he gets a dementia diagnosis.