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(CNN) —  

Michael Bloomberg, the billionaire former New York City mayor and potential 2020 presidential candidate, announced Wednesday that he re-registered as a Democrat, saying the party must “provide the checks and balances our nation needs so badly.”

“At key points in U.S. history, one of the two parties has served as a bulwark against those who threaten our Constitution,” Bloomberg wrote in an early morning Instagram post.

“Two years ago at the Democratic Convention, I warned of those threats. Today, I have re-registered as a Democrat – I had been a member for most of my life – because we need Democrats to provide the checks and balance our nation so badly needs.”

A Bloomberg spokesman declined any further comment.

Bloomberg, who was elected mayor as a Republican and an Independent, has been toying with the idea of running for president in 2020 as a Democrat. In September, he told The New York Times that if he were to run in two years, it would only be on the Democratic ticket.

“I’m just way away,” Bloomberg told the paper, “from where the Republican Party is today,” adding that he also doesn’t fall in line with all of the Democratic Party’s politics.

Bloomberg also explored a 2016 presidential bid as an independent but ultimately decided against it, writing in an op-ed that “an independent candidacy would split the Electoral College and allow Congress to elect an extremist.”

Nearly a week after telling the Times that he is considering a 2020 bid, he said in an interview on CNN’s “Fareed Zakaria GPS” that his focus right now is on this year’s elections.

“Right now, I’m only focused on the midterms,” Bloomberg said. “I believe that the Republicans have not done what they should have done in terms of providing some counterbalance to the executive branch.”

He went on to add, “Afterwards, you take a look at it.”

Bloomberg, whose wealth was amassed in part from media and software ventures, announced a plan in June to spend $80 million on the midterm elections, throwing most of his financial weight behind Democrats in their effort take control of the House of Representatives next month. Last week, he announced he was putting $20 million behind Democratic efforts to flip the Senate.

CNN’s Rebecca Berg, Elit Watkins, Dan Merica and Terence Burlij contributed reporting.