Former Colorado governor and current U.S. Senate candidate John Hickenlooper got into a fiery exchange on Sunday with an environmental activist who was protesting his past support for the oil and natural gas industry.

After leaving a Democratic Senate candidate forum in Longmont, Hickenlooper was confronted by a member of the Sunrise Movement who wanted to know why his administration joined a lawsuit suing the community for banning fracking, prompting an exasperated response from Hickenlooper that nearly turned physical.

Hickenlooper has established himself as the firm favorite in the Democratic primary for Senate after ending his presidential campaign in August but has faced constant criticism from liberal green groups who oppose his energy polices, opening up sharp divisions within the party.

The activist from the Sunrise Movement asked Hickenlooper to “respond” and “apologize” for joining the lawsuit, before Hickenlooper interrupted him, saying, “No. No. No. Shh. Hold on. Shh. Shh. Shh.”

As the activist continued to speak, Hickenlooper told him “don’t shout at me,” before the activist asked him, “How can we trust you to fight for the people in the climate crisis when you continually support oil and gas executives?”

Hickenlooper then grew increasingly frustrated and put both hands on the activist’s shoulders and repeatedly said, “Will you listen?”

At the point, Hickenlooper disengaged and left the room without saying anything more as the activist asked, “How can we trust you to fight for us Governor Hickenlooper?”

The full exchange was posted on Twitter by the Sunrise Movement with a message that said, “Gov. Hickenlooper thinks he can away with suing his own constituents AND still get enough support to run for congress. No one who would put people’s lives at risk for the sake of helping big oil execs deserves to be in office. We demand better.”

The Sunrise Movement has received funding from wealthy anti-fossil donors including the Rockefeller Brothers Fund and the group has endorsed Hickenlooper’s closet competitor in the primary, former state house speaker Andrew Romanoff and is deploying five full-time, paid staff to the state.

A sense of inevitability has taken hold in the race ever since Hickenlooper joined. A September poll showed Hickenlooper leading Romanoff by a massive 51 points and the Democratic Senatorial Campaign endorsed the former governor consolidating the party’s formal support around him.

But the Sunrise Movement hasn’t yet accepted Hickenlooper’s victory, tweeting, “Why should young people concerned for their future settle for this guy?”

Other candidates in the race have expressed similar frustration towards Hickenlooper who they feel is riding the legacy of his tenure as mayor of Denver and then governor, and many blasted him for failing to attend a climate change forum in Colorado Springs in October.

In the preparation for the forum on Sunday where Hickenlooper was confronted, Trish Zornio, another candidate, was heard on a hot mic (1:57 mark) telling the moderator that the Democratic establishment won’t allow full debates to protect Hickenlooper.

“Well, we haven’t had any debates actually because the party is not allowing us to debate because that might make a certain person not look as good,” Zornio said.