The move was an about-face for Bloomberg who said in March he would not make a 2020 run for the White House.
"I'm a New Yorker, and I know a con when I see one", he said dismissively of Trump during the 2016 presidential campaign. We can not afford four more years of President Trump's reckless and unethical actions.
But the debate stumbles of Mr Biden, 77, coupled with the unexpected strength of the twin far-left candidacies of Sen Warren, 70, and Sen Sanders, 78, left Mr Bloomberg and his advisors anxious Democrats could select a nominee unable to beat President Trump, 73, in 2020, sources told The Post.
"I think this is a structure that can cope with many eventualities", Micklethwait wrote.
Bloomberg joins a crowded field for the Democratic nomination, which included 10 in last week's debate in Atlanta and seven others who didn't qualify, including Deval Patrick, who announced his candidacy on November 14.
Ranked by Forbes as the eighth-richest American with an estimated worth of $53.4 billion, Mr. Bloomberg joins activist Tom Steyer as the second billionaire to enter the Democratic race and will have the advantage of being able to self-finance his campaign and pour millions of dollars into advertising and hiring staff.
With a personal fortune of $50 billion, Bloomberg's candidacy will likely shake up the open race, with 17 candidates already vying to be the Democratic nominee to take on Trump next year.
He points to his successes as an executive who helped revitalize post-9/11 NY, his advocacy and financial support for gun control and his work on climate change.
Bloomberg, who has a Master of Business from Harvard, is a philanthropist and owns Bloomberg News.
Several weeks ago, amid reports he might run, Trump offered a hint at what he'd be calling Bloomberg.
The ads will reportedly begin airing as early as Monday.
Some Democratic leaders are growing increasingly concerned that a nasty primary fight won by the party's progressive and liberal wings could give Mr Trump a chance to gain ground in during the northern spring and summer of 2020.
Bloomberg's impending decision comes little more than two months away from the first-in-the-nation Iowa caucuses, with the New Hampshire primary only a week after.
No winning presidential contender has ever pursued a similar strategy.
"America already elected a builder", Conway said, referring to Trump. I wish he'd be mayor of New York City again.
Bloomberg joins an already crowded field of candidates who have been showing up for debates for months and in some cases, campaigning for nearly a year, He apparently assumes he can just spend a lot of money and people will forget that he's a billionaire who supported stop and frisk in NY.
Conway cast doubt on whether he'd be welcomed by Democratic voters.