Combatting climate change and preserving the environment is a top issue for Democratic voters — especially progressives. But in Colorado, it’s dividing Democrats in the race for U.S. Senate.

Former Colorado Governor John Hickenlooper recently abandoned his long-shot bid for the White House to enter the Democratic primary to decide who’ll face off against incumbent Republican Cory Gardner in 2020.  Gardner’s considered one of the most at-risk incumbents in next year’s election.

Although Hickenlooper — a popular, two-term governor– is favored to win his party’s nomination, the divisions among Colorado Democrats over his views on climate and energy are a microcosm of growing dissension within the Democratic Party on a national scale.

After the Colorado Democratic Party endorsed Hickenlooper’s senate bid, the Denver Post obtained internal emails from the CDP showing many climate-conscious progressives are unhappy about the endorsement. The chair of the Douglas County Democratic Party, Dana Torpey-Newman, said she felt like other, better candidates — including an environmental activist and a former U.S. Energy Department official — were being “forced out” by the Democratic establishment.

The sticking point with Hickenlooper for some Colorado Democrats is his approach to climate change and the environment. Hickenlooper worked in the oil and gas industry as a geologist before he ran for office. As governor, he was friendly to the industry and promoted the controversial practice of hydraulic fracturing, or fracking, to obtain natural gas, which many local municipalities in Colorado oppose.

In an effort to show what he considers fracking harmless, Hickenlooper famously drank a glass of fracking fluid from the oilfield services company Halliburton, describing it as a “benign” fluid.

Many scientists and environmentalist organizations like Environment America, which has a Colorado chapter, condemn fracking as not only harmful to the earth but also toxic to humans. Some studies have found a 30 percent increase in air pollution around fracking sites, as well as a 27 percent increase in hospitalizations.

Industry advocates dispute those claims, while noting that fracking has helped bring U.S. carbon dioxide emissions to near their lowest point in 25 years.

According to Environment America, more than 500 municipalities successfully passed local ballot measures banning fracking in their areas.

That’s what some Colorado municipalities tried to do. Hickenlooper threatened to sue them, and followed through on one case: the state of Colorado joined oil and gas companies in a lawsuit against the city of Longmont, Colorado for passing a local ban on fracking, even after Hickenlooper assured Longmont residents the state wouldn’t join the lawsuit.

Hickenlooper’s stance was shared by most Obama-era Democrats: Obama famously praised fracking because natural gas burns more cleanly than coal and results in cheaper energy costs.

But two of the frontrunners in the Democratic presidential primary race — Elizabeth Warren and Bernie Sanders — plan to ban fracking if they win the presidency, much to the satisfaction of the growing progressive wing in the Democratic Party.

“Fracking activists have dubbed Hickenlooper ‘Frackenlooper’ for his support for fracking,” said Karen Breslin, a political science instructor with expertise in environmental policy at the University of Colorado Denver, and a former community rights lawyer and energy reporter for the Bureau of National Affairs. “Do I think he’s a pro-environment candidate? I most certainly do not. He’s a centrist corporate Democrat.”

Breslin thinks Colorado as a state is too friendly toward the oil and gas industry, and that Hickenlooper’s green policies — like his clean car standards — are just a front to curry favor with voters.

“All of the communities that have oil and gas resources are under pressure, and the industry is very aggressively trying to develop those resources,” she told InsideSources.

A Colorado political consultant who declined to be named due to his involvement in the senate race told InsideSources he thinks the animosity towards Hickenlooper is unwarranted, and praised the former governor’s environmental record.

“He gets a bad rap in part because of his friendships on the Republican side and in the business community and the oil and gas community,” he said. “And that’s what you would expect from someone who was in the oil and gas business. He’s actually stepped in and tried to negotiate so that we don’t have a huge fight between the left wing of the environmental movement and the middle of the road folks.”

An independent political consultant said in 2014 that Hickenlooper prefers to negotiate and try to find balance between warring factions. In 2011, The Colorado Independent ran a story with the headline “Gov. Hickenlooper earns praise from business interests, environmentalists” with his New Energy Economy plan.

But eight years later, climate-focused Democrats are losing patience with approaches like Hickenlooper’s given recent new reports projecting the effects of climate change.

“Balance is a code word for continuing to do what we’re doing,” Breslin said.

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