A video released on Sunday by former New York City Mayor Michael Bloomberg marks the official start of the billionaire’s 2020 presidential run, a top adviser to Bloomberg told Fox News.

The one-minute ad, which was posted on social media and features images of Bloomberg campaigning alongside those during his younger years, shots of New York City and unflattering images of President Trump, is “the launch ad,” according to one of his top advisers.

Along with the video, Bloomberg posted a written statement on his campaign website in which he laid out why he was the best candidate to defeat President Trump next November.

“I’m running for president to defeat Donald Trump and rebuild America,” Bloomberg wrote.

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“We cannot afford four more years of President Trump’s reckless and unethical actions,” he continued. “He represents an existential threat to our country and our values. If he wins another term in office, we may never recover from the damage.”

There has been speculation for months that Bloomberg, who donated millions of his own dollars to Democratic candidates in the 2018 midterm elections, would enter the 2020 fray, but rumors hit a frenzied point earlier this month when he completed the paperwork to be on the Democratic primary ballot in Alabama.

Bloomberg had announced earlier this year that he would not seek the party's nomination. But, in a statement obtained by Fox News in early November, his political adviser Howard Wolfson said Bloomberg was worried that the current crop of Democrats seeking the White House was "not well-positioned" to defeat President Trump.

"In 2018 [Bloomberg] spent more than $100 million to help elect Democrats to ensure that Congress began to hold the President accountable," Wolfson said. "And this year he helped Democrats win control of both houses of the Virginia legislature."

He added: "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."

Bloomberg's expected move has come amid increasing concern about the leftward drift of the major Democratic candidates, the departure of candidates who failed to gain traction – and talk of other potential late entries.

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Bloomberg’s entrance comes just 10 weeks before primary voting begins, an unorthodox move that reflects anxiety within the Democratic Party about the strength of its current candidates.

As a centrist with deep ties to Wall Street, Bloomberg is expected to struggle among the party’s energized progressive base. He became a Democrat only last year. Yet his tremendous resources and moderate profile could be appealing in a primary contest that has become, above all, a quest to find the person best-positioned to deny Trump a second term next November.

Forbes ranked Bloomberg as the 11th-richest person in the world last year with a net worth of roughly $50 billion. Trump, by contrast, was ranked 259th with a net worth of just over $3 billion.

Already, Bloomberg has vowed to spend at least $150 million of his fortune on various pieces of a 2020 campaign, including more than $100 million for internet ads attacking Trump, between $15 million and $20 million on a voter registration drive largely targeting minority voters, and more than $30 million on an initial round of television ads.

Even before the announcement was final, Democratic rivals like Bernie Sanders pounced on Bloomberg’s plans to rely on his personal fortune.

“I’m disgusted by the idea that Michael Bloomberg or any billionaire thinks they can circumvent the political process and spend tens of millions of dollars to buy elections,” Sanders tweeted on Friday.

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Elizabeth Warren, another leading progressive candidate, also slammed Bloomberg on Saturday for trying to buy the presidency.

"I understand that rich people are going to have more shoes than the rest of us, they're going to have more cars than the rest of us, they're going to have more houses,” she said after a campaign stop in Manchester, New Hampshire. “But they don't get a bigger share of democracy, especially in a Democratic primary. We need to be doing the face-to-face work that lifts every voice."

Fox News’ Ed Henry and The Associated Press contributed to this report.