Michael Bloomberg announced Wednesday that he had re-registered as a Democrat, in a sign that the former New York City mayor could be seriously considering a presidential bid in 2020.

“At key points in U.S. history, one of the two parties has served as a bulwark against those who threaten our Constitution. Two years ago at the Democratic Convention, I warned of those threats,” Bloomberg announced in a post on Instagram that he also shared on Twitter.

“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,” he added.

Bloomberg had been a Democrat prior to his initial mayoral run in 2001, when he became, and was elected as, a Republican. He was re-elected in 2005 as a Republican, but then became an independent in 2007 and was re-elected to a third term in 2009 as an independent.

He spoke in support of Hillary Clinton at the 2016 Democratic National Convention.

Bloomberg flirted with presidential runs in 2008, 2012, and 2016, but ultimately decided not to jump in each time.

Last month, The New York Times and The Times of London both reported that Bloomberg, 76, was seriously considering running for president in 2020 as a Democrat.

The former mayor, who previously made a fortune as the founder of media and finance company Bloomberg LP, pledged earlier this year to spend $80 million on efforts to help flip the House for the Democrats.

CORRECTION (Oct. 10, 2018, 11:42 a.m. ET): An earlier version of the article misstated the amount of money former New York City Michael Bloomberg plans to contribute to Democratic efforts to win the House. It is $80 million, not $80 billion.