NATIONWIDE — Former New York Mayor Michael Bloomberg announced on Sunday that he is joining the Democratic candidates as a presidential hopeful.

"I’m running for president to defeat Donald Trump and rebuild America," the 77-year-old businessman tweeted.

In the video that accompanies his tweet, it stated that "… when New York suffered the terrible tragedy of 9/11, he took charge, become a three-term mayor who brought a city back from the ashes, and brought back jobs and hope with it."

It should be noted that Rudy Giuliani was not eligible for re-election because New York City limits the mayoralty to two consecutive terms.

Giuliani was mayor of New York from Jan. 1, 1994, to Dec. 31, 2001.

Bloomberg was a Democrat, but switched to the Republican Party during his first run for mayor in 2001.

After he won a second term in 2005, he left the GOP two years later and campaigned to change the term limits for the city's mayor.

The former Wall Street trader and self-made billionaire won a third term in 2009 as an independent candidate.

He is already pledge to spend his personal fortune on the 2020 race, and already buying more than $30 million in television ads in some key states.

He joins a long list of Democrats trying to pitch themselves as the party's frontrunner.

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 more than $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.

He did not say how much he would be willing to spend overall on his presidential ambitions, but senior adviser Howard Wolfson did: "Whatever it takes to defeat Donald Trump."

Wolfson also said that Bloomberg would not accept a single political donation for his campaign or take a salary should he become president.

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.

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."

Bloomberg does not speak in his announcement video, which casts him as a successful businessman who came from humble roots and ultimately "put his money where his heart is" to effect change on the top policy issues of the day — gun violence, climate change, immigration and equality, among them.

Bloomberg has devoted tens of millions of dollars to pursue his policy priorities in recent years, producing measurable progress in cities and states across America. He has helped shutter 282 coal plants in the United States and organized a coalition of American cities on track to cut 75 million metric tons of carbon emissions by 2025.

But he is far from a left-wing ideologue.

Bloomberg has declined to embrace Medicare for All as a health care prescription or the "Green New Deal" to combat climate change, favoring a more pragmatic approach.

The Associated Press contributed to this story.