WASHINGTON – Former Mayor Mike Bloomberg has tapped his immense fortune to help Democrats retain control of the US Senate.

Bloomberg has contributed $2.5 million into the Senate Majority PAC, a super PAC headed by former aides to Senate Majority Leader Harry Reid (D-Nev.), who faces a tough fight this year to hold on to his narrow 55-45 majority, largely due to damage done to Democrats by the ObamaCare mess.

Bloomberg’s generous contribution to the Senate Democrats’ cause “arose out of the close relationship the mayor has developed with Leader Reid over the years working on issues of concern to New Yorkers like [Hurricane] Sandy relief and gun safety,” Howard Wolfson, a former deputy mayor and close aide, told Politico.

One of the richest men in the world with a personal fortune valued at more than $27 billion, Bloomberg appears ready to bankroll more campaigns.

“Mike Bloomberg has made clear that he will continue to fight for the causes that matter to New Yorkers, even more so now that he isn’t constrained by the mayoralty,” said Wolfson.

Bloomberg’s billions could alter the playing field for this year’s and future elections, potentially countering the influence of Republican mega donors Charles and David Koch.

Bloomberg’s contribution to the Senate Majority PAC in some ways serves as a pay back for his recent Mayors Against Illegal Guns campaign that hurt Democrats in pro-gun states, including Alaska Sen. Mark Begich, Louisiana Sen. Mary Landrieu and Arkansas Sen. Mark Pryor.

Perhaps coincidentally, Senate Majority PAC has already started running TV ads to boost all three of those Democrats.