Former New York City Mayor Michael Bloomberg is strongly considering a run for the 2020 U.S. Democratic presidential nomination, a move that could greatly disrupt the field just three months before the first nominating contests. 

Bloomberg, the billionaire media mogul and philanthropist who served three terms as mayor of America's largest city, is skeptical that any of the current crop of Democratic candidates can defeat Republican President Donald Trump in next year's general election, a spokesman said.

"Mike is increasingly concerned that the current field of candidates is not well positioned to" beat Trump, Bloomberg spokesman Howard Wolfson said in a statement.

Bloomberg, 77, is expected to file paperwork this week to run in the Democratic presidential primary in Alabama, which has an early deadline for qualifying for the ballot. That would keep his options open for a possible White House bid, a source familiar with his thinking told Reuters.

Responding to the news, Trump on Friday taunted the move, saying "he's not going to do well but I think he's going to hurt (former U.S. President Joe) Biden actually."

"There's nobody I'd rather run against than little Michael," Trump said, adding that "little Michael will fail."

The Democratic field, now numbering 17 candidates, has coalesced into four top contenders according to recent polls: U.S. Senators Elizabeth Warren and Bernie Sanders, who represent the party's progressive wing, and former Vice President Joe Biden and Mayor Pete Buttigieg, of South Bend, Indiana, representing the more moderate wing.

Bloomberg, the chief executive officer and founder of Bloomberg L.P., served as New York's mayor from 2002 to 2013 and has been a leading advocate and philanthropist on the issues of climate change and gun violence.

"If Mike runs, he would offer a new choice to Democrats built on a unique record running America's biggest city, building a business from scratch and taking on some of America's toughest challenges as a high-impact philanthropist," Wolfson said.

"Mike would be able to take the fight to Trump and win."