Former New York City Mayor Michael Bloomberg has taken a first step towards potentially joining the race for the White House, registering as a candidate in the Alabama Democratic primary race.

The billionaire media mogul, who has not formally confirmed his candidacy, submitted on Friday the documents to meet Alabama’s filing deadline.

Bloomberg, who served as New York’s mayor from 2002 to 2013, is sceptical 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, Howard Wolfson said in a statement.

Progressives vs moderates

The Democratic field, now numbering 17 candidates has coalesced into four top contenders according to recent polls: US 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 LP, has been a leading advocate and philanthropist on the issues of climate change and gun violence.

Analysts say a Bloomberg candidacy could do the most damage to the prospects of Biden, who is seen as the frontrunner. Commenting on Bloomberg’s potential candidacy, the former vice president said he was not worried the media mogul would draw away centrist voters.

“Michael’s a solid guy,” Biden told reporters in Concord, New Hampshire, while registering to take part in the February primary in the northeastern state.

“I have no, no problem with him getting in the race,” Biden said. “And in terms of he’s running because of me, last polls I looked at I’m pretty far ahead.

“If I’m not mistaken I’m doing pretty well, both relative to Trump and relative to all the people running,” he said.

Bloomberg has been critical of Warren and her plan to institute a tax on the super-rich if she is elected as president to fund programmes ranging from universal healthcare to free college tuition.

Tom Steyer, a billionaire candidate from California who has made climate change a centrepiece of his campaign, has spent millions only to see his bid languish amid criticism from his rivals for trying to buy his way into the election.

“More billionaires seeking more political power surely isn’t the change America needs,” said Sanders’ campaign manager, Faiz Shakir.

Warren responded to the news of Bloomberg’s move by tweeting at him with a link that showed how much he would pay under her wealth tax.

Bloomberg, whom Forbes ranks as the eighth-richest American with an estimated worth of $53.4bn, would be able to largely fund his campaign himself, perhaps allowing him to ramp up his candidacy quickly. Still, he would have to build a multistate organisation on the fly.

At age 77 he would be the second oldest candidate among the Democratic contenders, behind Sanders, who is 78. Biden is 76 and Warren is 70. On the Republican side, Trump is 73.

The Iowa caucuses, the first nominating contest on the Democratic primary calendar, will be held on February 3.