Biden has been the "perceived front runner" only because he seems "safe" to a fairly significant portion of timid voters who fear change.

"Let's go back to how everything was in 2008" is not a very inspiring campaign theme for Democrats, although when you think about it a bit that would be great. At least compared to four more years of Trump.

If Biden wants to win, he has to unite everybody left of Trump by asking a progressive to be his VP. If a progressive wants to win, they need to ask a centrist to be their VP. This is no time to fly off in different directions, IE. the usual Democratic fiasco. First of all you need to WIN, and then you can enact your agenda. Lose and you can preach your agenda into the wind for the next four years. Unless you wind up in a concentration camp for insulting the King.