Mike Bloomberg is a Democrat. Again. The billionaire former New York mayor, who is considering a run for the White House in 2020, announced on social media early Wednesday that he re-registered as a member of the Democratic Party. He had previously run for office as a Republican and an independent. In his Instagram post, Bloomberg cited a need for a check on power in Washington. The Republican Party holds the White House and Congress, and the Supreme Court has a widely perceived conservative majority now that Brett Kavanaugh has been confirmed. "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 wrote on Instagram. "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 also took to Twitter. The move comes as no surprise. Bloomberg has said he would shell out millions of dollars to support Democrats as they try to grab majorities in Congress in next month's midterm elections. Earlier this month, a super PAC funded primarily by Bloomberg spent more than $2 million in support of seven Democratic women looking to unseat Republicans in House races. That came after his pledge to invest $80 million to support Democratic congressional candidates this year. He also said he would donate $20 million to a super PAC dedicated to getting Democrats elected to the Senate. While he considers a run against President Donald Trump, Bloomberg has some work cut out for him if he wants to appeal to the base of his new party. While Bloomberg, who has previously flirted with the idea of running for president, has positioned himself as a socially progressive billionaire, advocating for gun control and environmentalist policies, he has taken some stances that might not be palatable to rank-and-file Democrats. In a recent New York Times interview, he chided liberals for pushing aggressive regulatory policies on big business and major banks. Sens. Elizabeth Warren and Bernie Sanders, both considered potential contenders for the Democratic nomination in 2020, are popular among the party's base. Bloomberg has also defended the "stop and frisk" tactics once used by police in New York before a federal judge ruled that the policy was being applied in an unconstitutional manner. It's an issue on which Bloomberg shares some common ground with Trump, who called for its use in Chicago to reduce violent crimes there. "Stop and frisk works," the president said earlier this week at a police chiefs convention.