Furthering deepening the divide within the U.S. Senate Democratic primary in Colorado, opposing candidates and environmental activist groups across the state have sharply criticized former Gov. John Hickenlooper for declining to attend a forum focused on climate change this weekend.

The event – “Planet in Peril” – is sponsored by 350 Colorado, Keep Colorado Green, and Indivisible Colorado Environment Action among others and will take place this Sunday in Colorado Springs where organizers say it will raise awareness around climate change and to “make sure the candidate we elect is 100% serious” about the issue. The organizers have said it’s open to all U.S. Senate candidates but Hickenlooper’s campaign cited a “scheduling conflict,” according to a report from Colorado Public Radio.

Every other Democratic running in the primary will attend and they have taken the opportunity to blast Hickenlooper for his absence.

“Disappointed to hear this,” tweeted Andrew Romanoff, one his Hickenlooper’s top rivals in the race. “You can’t dodge this debate – or frack your way to a clean-energy future,” he continued.

Fellow candidate Diana Bray said Hickenlooper isn’t attending because he doesn’t want to defend his record of supporting oil and natural gas development.

Activists groups with a reputation for no-compromise tactics have also piled on Hickenlooper.

“This is clearly more smoke and mirrors from a career politician who has no intention of addressing the climate crisis as evidenced by his lack of urgency to attend,” said 350 Colorado, one of the forum’s sponsors.

The Colorado chapter of the Sunrise Movement said, “Hickenlooper used ‘schedule conflicts’ to not show up at the Denver Climate Strike, and now he’s using it as an excuse to skip the CO climate debate? Admit it, you’re afraid to show up because you don’t have any real ideas to address this crisis.”

Similarly, Joe Salazar, the executive director of Colorado Rising, mocked Hickenlooper’s absence with an offer to replace him on stage by tweeting, “I can stand in for him (in parody) and discuss his wonderful relationship with O&G buddies and how he championed lawsuits against communities and placed fracking rigs outside babies’ homes and schools.”

Criticism for Hickenlooper has also come from outside the state as well. Prominent liberal commentator Cenk Uygur whose is based in Los Angeles, dredged up the former governor’s litigation against anti-fracking activists.

“It’s actually worse than that. Hickenlooper has threatened to sue any local district that would take action against #ClimateEmergency by banning fracking. He will protect oil & gas from anyone fighting back,” Uygur tweeted.

Hickenlooper’s entry into the Senate race after ending his presidential campaign in August has already forced out several, more moderate Democratic competitors, but liberal rivals have continued along, highlighting the sharp divide between the two factions of the party.

The popular former two-term governor has bore the brunt of repeated attacks for his long support of oil and natural gas development. Westword – a Denver magazine opposed to fossil fuel use – recalled Hickenlooper’s consistent push to boost production during his eight-year tenue in what the magazine says came at the expense of neighborhood groups support for stronger environmental and health regulations.

Westword even brought up his “Frackenlooper” nickname that’s constantly used by activists who oppose his energy policies.

Hickenlooper has often felt much of the criticism directed towards him has been unfair. In opposing Prop 112 last year – the ballot initiative to increase the setback distance from homes and schools – he claimed Colorado’s regulations were the toughest in the nation on methane emissions and disclosure of chemicals and he said that his administration enacted numerous rules governing production.

In addition to touting his support for stronger regulations, he also worked to build relationships with big money environmental donors by praising Tom Steyer’s leadership to elect anti-oil and gas candidates to Congress.

Mistrust from the environmental crowd hasn’t damaged Hickenlooper’s campaign in the early days of the race however. A poll conducted by PPP in early September found that he had the support of 60 percent of Democrats, with a second-place Romanoff far behind at 9 percent.