In recent days, he has created a presidential campaign committee with the Federal Election Commission and qualified for the primary ballot in at least three states.
He announced earlier in November a $100 million online ad campaign targeting Mr. Trump in four battleground states.
For weeks, Bloomberg News' top editors have wrestled with how they could fairly report on their boss if he made a decision to run while being fair to his political rivals, including President Trump, who is seeking a second term.
Bloomberg will count on leveraging his fortune - Forbes ranks him as the 15th richest person in the world now - to make up ground on the favorites. "You've got the front runners saying that we don't want any billionaires in the country, let alone in the Democratic primary". "If you can't build grassroots support for your candidacy, you have no business running for president". Several candidates, including Sens.
Because of his late entry into the race, Bloomberg will mount an "unconventional primary campaign", the New York Times reported, by ignoring the earliest primary and caucus states in February to instead focus on "delegate-rich March primaries in states such as California and Texas".
Right now, he adds that they have reporters continuing to "investigate the Trump administration, as the government of the day".
"I think this is a structure that can cope with many eventualities", Micklethwait wrote. That is a record for the amount of money ever spent by a presidential candidate in seven days.
Bloomberg's team insists that his wealth allows him to be more responsive to the concerns of everyday people because he isn't beholden to special interests.
"We can not afford four more years of President Trump's reckless and unethical actions", Bloomberg wrote in an announcement on his campaign website.
Bloomberg faced criticism from others for buying more than $30 million in ads for his campaign. Pete Buttigieg, the 37-year-old mayor of South Bend, Indiana, has broken into a solid lead in Iowa with similarly centrist views, but lags in single digits in national polls and in predominantly non-white areas. The rules of entry, as set by the Democratic National Committee, now require participants to meet a polling threshold and raise donations from tens of thousands of voters.
The ad blitz places Bloomberg's sprawling media empire in the uncomfortable, and perhaps unprecedented, position of having to cover the campaign of the man who founded and still heads their company.
How much is he willing to spend?
"I know what it takes to beat Trump, because I already have".