Mike Bloomberg announced Wednesday that he is changing his voter registration to Democrat — a possible signal that he’s weighing a presidential run 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 said in a statement posted to Instagram,Twitter and Facebook.

“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.”

Bloomberg, 76, was a Democrat before he enrolled in the Republican Party to run for New York City mayor in 2001.

In 2007, he left the Republican Party and declared himself a registered independent or unaffiliated voter as the party swung to the right.

The billionaire business mogul — who endorsed Hillary Clinton over President Trump in the 2016 election — is heavily invested in helping elect Democrats in congressional midterm elections on Nov. 6. He has vowed to spend at least $100 million — $80 million on House races and $20 million on Senate races.

Worth an estimated $50 billion, Bloomberg is a social liberal who is in sync with the Democratic Party on issues like gun control, immigration, abortion rights and climate change.

But he’s also a corporate Democrat who’s to the right of the growing socialist-progressive wing of the party on issues like taxation and policing. As the Big Apple’s three-term mayor, he was a staunch backer of stop-and-frisk policing.

He has said he would make a decision on the presidency after the midterm elections.