Michael R. Bloomberg, the former New York City mayor and presidential candidate, announced Sunday that he planned to spend $100 million in Florida in the coming weeks to support Joseph R. Biden Jr.’s presidential candidacy.
The pledge came as new polls showed a particularly tight race between Mr. Biden and President Trump in Florida, a key battleground state that carries 29 electoral votes.
The announcement also followed criticism from within the Democratic Party — in spite of a huge $18 million transfer to the Democratic National Committee this spring — that Mr. Bloomberg had not delivered on his promise to put the full weight of his fortune behind the general-election effort to defeat Mr. Trump.
The commitment in Florida, while enormous for a one-state program, represents a significant pullback from the promises made by some Bloomberg advisers during primary season. Mr. Bloomberg’s campaign manager, Kevin Sheekey, had told Democrats privately that if Mr. Bloomberg were not the nominee he would form a new super PAC and mount an enormous effort against Mr. Trump in the country’s biggest swing states.