Michael Bloomberg, ex-New York City mayor, won't run for president in 2020

Former New York City Mayor Michael Bloomberg ended months of speculation Tuesday about his political aspirations when the 77-year-old billionaire said he would not join the crowded field of Democratic candidates for president.

The one-time Republican who is now a registered Democrat and prominent critic of President Trump spent much of last year testing the political waters.

"I know we can do better as a country," he said in a Bloomberg News editorial. "And I believe I would defeat Donald Trump in a general election. But I am clear-eyed about the difficulty of winning the Democratic nomination in such a crowded field."

Bloomberg urged Democrats to unify behind a candidate who had a realistic chance in 2020 to beat the incumbent, and fellow New York City billionaire, in a thinly veiled reference to the far-left positions of most of the current Democratic Party's declared candidates.

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"It's essential that we nominate a Democrat who will be in the strongest position to defeat Donald Trump and bring our country back together," Bloomberg wrote. "We cannot allow the primary process to drag the party to an extreme that would diminish our chances in the general election and translate into 'Four More Years.'"

He spent more than $100 million to help Democrats in the 2018 midterm election.

The Associated Press contributed to this report