One Scotch & Joke
That doesn't explain where you've got this 'healthy leading total' from. At present Sanders is trailing Biden and the states where he was perceived to be strongest (New Hampshire, Vermont, California) have already voted. Biden is also picking up endorsements from all the candidates who've dropped out and whilst Warren is still in it, she's apparently been copping lot of abuse from both legit Bernie bros and the more sinister anonymous Bernie Bots for splitting the progressive vote so there's no guarantee she'll swing an endorsement Bernie's way either.
I agree that the deck would be stacked against him if went into convention with anything other than an outright clear majority but it's not looking like that'll even be a factor.