WASHINGTON — Michael Bloomberg, the billionaire former mayor of New York City, is opening the door to a 2020 Democratic presidential campaign, signaling his dissatisfaction with the current crop of candidates vying to take on President Donald Trump.

Bloomberg, who initially ruled out a 2020 run, has not made a final decision on whether to jump into the race less than three months before primary voting begins, according to advisers. But he is taking steps toward a campaign, including filing to get on the ballot in Alabama's presidential primary. Alabama has an early filing deadline and is among the states that vote on Super Tuesday, named for the large number of state contests that day.

In a statement on Thursday, Bloomberg adviser Howard Wolfson said the former mayor is worried that the current crop of Democratic presidential candidates is "not well positioned" to defeat Trump.

With immense personal wealth, Bloomberg could quickly build out a robust campaign operation across the country. The 77-year-old would pose an immediate ideological challenge to former Vice President Joe Biden, who is running as a moderate and hopes to appeal to independents and Republicans who have soured on Trump. But the billionaire media mogul with deep Wall Street ties could also energize supporters of liberal candidates Elizabeth Warren and Bernie Sanders, who have railed against income inequality and have vowed to ratchet up taxes on the wealthiest Americans.

"He's a literal billionaire entering the race to keep the progressives from winning," said Rebecca Katz, a New York-based liberal Democratic strategist. "He is the foil."

Bloomberg is a former Republican-turned independent who registered as a Democrat last year. He actively supported Hillary Clinton in 2016 and blasted Trump, his fellow New Yorker, as a con man who overinflates his business success.

Bloomberg has long flirted with a presidential run but never launched a campaign. He seriously considered a 2020 campaign, traveling to early voting states and conducting extensive polling, but ultimately passed in part because of Biden's expected strength in the field. Aides said they did not see room for two moderate contenders in the crowded Democratic primary field.

Bloomberg's decision to reconsider suggests he shares the concerns of other Democrats who are increasingly worried about the former vice president's fundraising and messaging, particularly as Warren's popularity has risen. Although Warren is a favorite of liberals, some Democrats worry that she would struggle to appeal to moderates and Republicans who may be seeking an alternative to Trump.

"There are smart and influential people in the Democratic Party who think a candidate like Bloomberg is needed," said Jennifer Palmieri, a senior adviser to Clinton. "But there is zero evidence that rank-and-file voters in the early states of Iowa and New Hampshire feel the same. Absent a desire from voters for a Bloomberg candidacy, it can be hard to get off the ground."

Bloomberg would have to swiftly make up ground to compete with candidates like Biden, Warren and others, who have spent months traveling the country meeting voters.

Warren on Thursday tweeted: "Welcome to the race, @MikeBloomberg!" and linked to her campaign website, saying he would find there "policy plans that will make a huge difference for working people and which are very popular."

Bloomberg appeared to be taking the first step by moving to file in Alabama, which votes on March 3.

A spokesman for the Arkansas Democratic Party said a person representing a "mystery candidate" reached out Thursday afternoon asking about the requirements to join the ballot in the state. Reed Brewer, communications director for the Arkansas Democrats, said he walked the individual through the process — which simply requires filing documentation with both the state party and secretary of state, as well as paying a $2,500 fee — and was assured that the fee would be "no problem" for the mystery candidate.

There is no filing requirement for a candidate to run in the Iowa caucuses, which are a series of Democratic Party meetings, not state-run elections. It means a candidate can enter the race for the Feb. 3 leadoff contest at any time.