NEW YORK (Reuters) - U.S. gun-control advocates have outspent by more than 40 percent gun-rights groups on next month’s congressional elections, reversing the National Rifle Association’s longstanding dominance in spending on gun politics.

FILE PHOTO: Gun enthusiasts looks over Smith & Wesson guns at the National Rifle Association's (NRA) annual meetings and exhibits show in Louisville, Kentucky, U.S., May 21, 2016. REUTERS/John Sommers II/File Photo

Boosted largely by the personal fortune of billionaire Michael Bloomberg, who is considering a 2020 presidential run, the gun-control war chest almost entirely benefits Democrats, who are seeking to wrest majorities from the Republicans in the House of Representatives and Senate in the Nov. 6 elections.

Graphic: U.S. gun-control spending - tmsnrt.rs/2PhSBxV

Gun-control groups, including Giffords and Everytown for Gun Safety, have spent $20.2 million on the elections, well over the $14.1 million spent by pro-gun groups led by the NRA, according to data released on Friday by the U.S. Federal Election Commission.

So far, it marks the first time in at least two decades that gun-control groups have outspent gun-rights groups on federal races, though gun-control groups have outspent gun-rights advocates in state elections in recent years, according to data compiled by the National Institute on Money in Politics.

“There is definitely a shift,” said Peter Ambler, the executive director of Giffords, formed by gunshot survivor and former U.S. Representative Gabby Giffords after the mass shooting in December 2012 that killed 20 school children in Connecticut. “It was just a few years ago when people considered gun safety to be one of politics’ third rails. Now the opposite is true.”

The FEC report covers federal campaign spending through Oct. 17 and will be the last public report before the Nov. 6 vote.

The NRA accounts for about 85 percent of the gun-rights spending and overwhelmingly supports Republicans. It could still close the gap as its Political Victory Fund had $8.9 million on hand as of Oct. 17, the FEC data showed, compared with $2.1 million for Giffords and Everytown combined.

An NRA spokeswoman said Bloomberg’s money would not overturn public support for the Second Amendment of the U.S. Constitution, which protects the right to keep and bear arms.

“While the gun-control lobby is funded by a blank check from a New York City anti-gun billionaire, the NRA relies on millions of small donations from working men and women,” NRA spokeswoman Jennifer Baker said in an email. “His money is no match for our grassroots organization.”

The NRA is concentrating on unseating Senate Democrats and recently said it would spend more than $1 million aimed at defeating U.S. Senator Joe Donnelly of Indiana.

Bloomberg, founder of the financial information and media company Bloomberg LP, formed Everytown in 2014 when he pledged $50 million to the cause and combined forces with Moms Demand Action for Gun Sense in America. Bloomberg has pledged another $100 million for House and Senate Democrats this year.

Everytown has spent $3.6 million, according to the FEC data. Most of its $20 million budget this year has been devoted to state races.

Giffords has spent $16.3 million this election cycle, the FEC data show, and has set aside at least $1 million for each of four competitive House races to defeat incumbent Republicans in Virginia, Minnesota, Texas and Colorado.

Everytown has pledged to spend $10 million in state races in Georgia, Michigan, Nevada and New Mexico, plus another $3.5 million in Nevada and $2 million in Florida.

Gun control groups have outspent the pro-Second Amendment forces in states before, notably in 2016, by a margin of $26 million to $11 million, according to National Institute on Money in Politics. The NRA and its allies more than made up for that with $70 million in spending on the federal level.