DENVER – Former New York City Mayor Michael Bloomberg is making a $1 million donation to an independent expenditure campaign supporting Democrat Mike Johnston for governor.

Both men have pushed tougher laws on guns. Bloomberg, the billionaire philanthropist and entrepreneur, has given more than $5 billion to such causes as climate change and gun control. Bloomberg is a co-founder of Everytown for Gun Safety and Mayors Against Illegal Guns. A former Democrat, he served two terms as mayor as a Republican. Bloomberg switched to independent and was elected to a third term in 2007.

“Mike Johnston stands out as an extremely effective leader in reducing gun violence,” Stu Loeser, a longtime spokesperson for Bloomberg, told Colorado Politics via email Sunday night.

“We need people like him in office now more than ever to push for common-sense gun safety measures.”

The Frontier Fairness PAC will report the Bloomberg boost on its next report due May 7.

Terrance Carroll, former Colorado House speaker and co-chair of the Frontier Fairness, provided a statement in response to Bloomberg’s help.

“As state senator, Johnston worked tirelessly to reduce gun violence and keep dangerous weapons out of the wrong hands,” Carroll said. “He has stood up to the NRA and will continue to do so when he is elected Governor of Colorado. It’s unfortunate that Stapleton and the other Republican candidates aren’t willing to do the same.”

Johnston’s platform on guns has four points:

As of the end of last year, the PAC had $420,000.

Of that, LinkedIn co-founder and venture capitalist Reid Hoffman put in $250,000. Frontier Fairness received a $100,000 donation from Eric Resnick and his wife, Sara. Resnick is the managing member, co-founder and chief executive of Denver-based KSL Advisors.

Vestar Capital Partners founder James P. Kelley gave the super PAC $50,000, records show.

Bloomberg’s largesse puts Johnston’s supporters on par or ahead of the super PAC supporting presumed Republican frontrunner Walker Stapleton, Better Colorado Now. Both candidates’ campaigns also are raising significant cash for the competitive, likely expensive primaries. Officially super PACs are unconnected to the campaigns but can support their efforts.

Andy George, a spokesman for Better Colorado Now, said his PAC isn’t depending on a few large donors but a broad coalition of influential leaders, saying he thinks it’s the largest coalition of Colorado business leaders to unite behind a candidate in recent history.

“BCN’s donors all agree that Walker Stapleton will bring fiscal responsibility to state government and will be the best governor to lead Colorado forward,” he said.

“No matter how much ‘super cash’ Mike brings into his super PAC, it won’t compare to Polis’ piggy bank and Kennedy’s caucus win. He’s going to need a lot more than a big influx of out-of-state liberal elitist cash to win the primary. His super PAC will have to spend every dime going after Polis, which will just provoke a bigger spend from his camp. This is going to get real ugly, real fast.”