Former New York City mayor Michael Bloomberg officially launched his bid for the 2020 Democratic presidential nomination on Sunday.

Bloomberg's belated entry into the race – just three months before the first of the state-by-state party nominating contests – reflects his skepticism that any of the other 17 Democratic candidates can unseat the Republican president.

"I'm running for president to defeat Donald Trump and rebuild America. We cannot afford four more years of President Trump's reckless and unethical actions," Bloomberg said in a statement announcing his candidacy.  

"If he wins another term in office, we may never recover from the damage." 

Who will Bloomberg target?

Bloomberg will compete with former vice-president Joe Biden, Mayor Pete Buttigieg and Senator Amy Klobuchar to become the moderate alternative to liberal senators Elizabeth Warren and Bernie Sanders.

The 77-year-old has won allies in the Democratic party with his advocacy and philanthropy on climate change and in fighting gun violence, pouring millions of dollars into groups pushing for more restrictive gun laws.

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The former mayor, who had said in March that he would not make a 2020 run for the White House, will face significant disadvantages because of his late start however, including playing catch-up with rivals who have been putting together campaign staffs for months.

To counter his late start, he plans to pursue the unorthodox strategy of skipping the four states with early nominating contests in February, beginning on February 3 in Iowa, and focus primarily on states that hold primaries and caucuses starting on so-called Super Tuesday on March 3.

Ranked by Forbes as the eighth-richest American with an estimated worth of 53.4 billion U.S. dollars, Bloomberg will have the advantage of being able to self-finance his campaign and pour millions of dollars into advertising and hiring staff. 

Bloomberg has come under fire from liberal critics who say he would be the wrong choice for a Democratic Party turning against corporate money in politics and dedicated to ending income inequality in America.

"We do not believe that billionaires have the right to buy elections," Sanders said in a Twitter post on Sunday. "That is why multi-billionaires like Michael Bloomberg are not going to get very far in this election."