Bloomberg’s big bet: Can money beat Biden's momentum?

In his brief three-month campaign for president, Michael Bloomberg poured nearly three-quarters of a billion dollars into building an advertising and data-mining juggernaut unlike anything the political world had ever seen.

But a big part of the strategy hinged on a wildcard named Joe Biden.

Biden’s resurgence after a dominant victory on Saturday in South Carolina has upset that calculation in the critical do-or-die sprint before “Super Tuesday,” when Democrats in 14 states vote for the candidate to challenge Republican Donald Trump in November’s election.

It wasn’t supposed to be...