Part-time Bermuda resident and billionaire businessman Michael Bloomberg could mount a last-minute challenge in the Democratic presidential primary race.

Sources said that Mr Bloomberg, who owns a home in Tucker’s Town and is a regular visitor to the island, was expected to file paperwork this week in Alabama — but that he has not yet made a decision to enter the race to face Donald Trump in next year’s election.

Howard Wolfson, an adviser to Mr Bloomberg, said on Thursday that the former Mayor of New York City had become concerned about the weakness of the Democratic field.

He added that Mr Bloomberg saw the President as an “unprecedented threat to our nation”.

Mr Wolfson said: “We now need to finish the job and ensure that Trump is defeated — but Mike is increasingly concerned that the current field of candidates is not well positioned to do that.

“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.”

Mr Bloomberg, 77, has prepared to enter presidential contests before.

He considered a nomination run earlier this year and also in 2016. It is understood that members of his staff are already in Alabama to gather signatures to qualify for the Democratic primary.

Mr Bloomberg and his staff called several prominent Democrats on Thursday to tell them he was considering a run, including former Nevada senator Harry Reid, the retired majority leader who is still a power broker in the early caucus state.

Mr Bloomberg’s team also contacted Gina Raimondo, the governor of Rhode Island and the chairwoman of the Democratic Governors Association.

Mr Reid said that Mr Bloomberg had not said he planned to run for president, but that the significance of the call was obvious.

He added: “It wasn’t just to wish me a good weekend”.

Analysts said that Mr Bloomberg would be a threat to Barack Obama’s former vice-president Joe Biden, a middle of the road candidate who has struggled to raise cash to fund his candidacy.

It is believed that Mr Bloomberg bowed out of the 2020 race because of Mr Biden’s apparent strength, but has become concerned that he is not on track to win the Democratic nomination.

It is also understood that he does not see the two leading liberals in the race, Elizabeth Warren a senator in Massachusetts and Bernie Sanders a Vermont senator, as potential winners against Trump.

Ms Warren, who has clashed with Mr Bloomberg over her proposals to tax the super-rich, said his potential run for the Democratic nomination was “another example of the wealthy wanting our government and economy to only work for themselves”.

She added: “It’s not enough just to have somebody come in, anybody, and say they’re going to buy this election.”

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

Advisers to Mr Bloomberg said he would likely make up his mind about the race within days, rather than weeks.

However, Michael Gray, the chairman of the Arkansas Democratic Party, said Mr Bloomberg’s wealth could make him an important wild card in the race.

Mr Gray added: “It shakes things up, obviously.”

A Fox News poll in late October found Mr Bloomberg faces more opposition than enthusiasm at the outset of the primaries.

Presented with Mr Bloomberg as a hypothetical entrant into the primary, 32 per cent of Democratic primary voters said they would never vote for him and 6 per cent of Democratic primary voters said they would definitely support him.

Mr Bloomberg could still opt against a run, even preliminary steps towards a campaign could damage Mr Biden’s challenge.

It understood the Biden campaign expected strong support from centrists Democrats, traditional party donors and sectors of the business community to push him across the line.