For a last minute entrance like Biden to win, Hillary would have to come out explicitly in his favor. Clinton would file an intention to release all her pledged delegates and then have it be known that she prefers they support the new candidate instead of Sanders.

“But there would be no guarantees, as released delegates are truly ‘free agents’ who can now vote for anyone they might want to on a First Ballot of Roll Call at the Convention (and there are no real sanctions against any now-ex-Hillary pledged delegate failing to accede to Hillary’s “preference” for Biden in this scenario,” Berg-Andersson told TheDC over email.

He added, “Yet: if Hillary could get, say, some 1800 of her now-2200+ pledged delegates to, instead, support Biden on Roll Call of the States on Presidential Nomination in Philadelphia toward the end of this month and, in addition, some 600 of the ‘superdelegates’ were to go along with this plan– well, there’s your 2383 necessary to nominate for Joe Biden in this hypothetical!”