WASHINGTON — Former New York City mayor Michael Bloomberg is positioning himself to enter the Democratic presidential primary, a longtime Bloomberg adviser confirmed to NBC News Thursday, though he has not yet made a final decision.

"Yes and yes," Kevin Sheekey wrote in an email responding to the questions about whether Bloomberg, 77, a billionaire businessman, was preparing to run and collecting signatures in Alabama, moves first reported by The New York Times on Thursday afternoon.

Bloomberg's rationale for getting in the race now would be that the field of Democrats isn't strong enough to beat President Donald Trump, according to his spokesman, Howard Wolfson, who noted that Bloomberg has helped fund Democratic congressional and state legislative campaigns.

"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," Wolfson said in a statement to NBC News. "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."

Bloomberg's wealth would allow him to compete without having to worry about the fundraising challenges faced by other candidates. But if he were to formally launch a presidential bid, it would almost certainly be a target for progressive rivals such as Sens. Bernie Sanders, I-Vt., and Elizabeth Warren, D-Mass., who have been running populist campaigns that argue the rich should be paying more to underwrite programs for the rest.

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Shortly after the news broke, Sanders tweeted simply: "The billionaire class is scared and they should be scared," though he did not clarify whether he was speaking about Bloomberg specifically. Asked directly about a potential Bloomberg campaign, Sanders campaign manager Faiz Shakir said that "more billionaires seeking more political power surely isn't the change America needs."

Bloomberg, one of the wealthiest men in the world and a popular three-term mayor of New York, has flirted with running for president before. But, after exploring a bid earlier this year, he announced in March that he would not run.

"I believe I would defeat Donald Trump in a general election," he wrote in an opinion column for the Bloomberg news service at the time. "But I am clear-eyed about the difficulty of winning the Democratic nomination in such a crowded field."

But that field has winnowed, and Bloomberg still sees himself beating Trump.

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

Alabama's Democratic Party chairman, state Rep. Christopher England, said Thursday night that he was unaware of a potential Bloomberg candidacy, noting the 5 p.m. CT (6 p.m. ET) Friday deadline. It’s still a possibility a new candidate could meet the requirements and submit paperwork before the deadline, England said.

To get on the Democratic presidential primary ballot in Alabama, a candidate must present 500 signatures from across the state or 50 signatures from each congressional district. The prospective candidate must also pay a $2,500 fee.