Updated 5:32 p.m.

A growing national movement of young climate activists has put former Colorado Gov. John Hickenlooper on notice.

On Monday, the Sunrise Movement endorsed former Democratic state House Speaker Andrew Romanoff in the primary for Colorado’s U.S. Senate race. The move is meant to unite Colorado progressives against Hickenlooper, who leads Romanoff and the other candidates in polls and fundraising in the race for their party’s nomination.

While the group has already endorsed Green New Deal co-sponsor Sen. Ed Markey in the Massachusetts primary, backing Romanoff is its first endorsement of a Senate challenger in the 2020 election. It also kicks off a national plan to sideline moderate Democrats in races that could decide control of the Senate.

Romanoff was thrilled to hear the news Monday morning. In a not-so-subtle dig against Hickenlooper, he said the endorsement will boost his candidacy and help build a path for ambitious climate policies in the U.S. Senate.

"Passing a Green New Deal won't be easy," he said. "But it will be impossible if not only Republicans, but Democrats as well, start echoing the talking points of the fossil fuel industry."

A spokesperson for Hickenlooper's Senate campaign said it had no comment on the endorsement.

To reinforce the move, Sunrise plans to launch a field operation in Colorado. A spokesperson with the organization said it should have five full-time paid organizers in the state by the spring. More could be added as the primary heats up.

“We're going to be mobilizing on college campuses and around schools to make sure that every young person in Colorado uses their vote for Andrew Romanoff,” said Boulder Sunrise Coordinator Michele Weindling. “And we're going to also be highlighting all the reasons why Hickenlooper is so dangerous for this state.”

Weindling knows that sounds like big talk from a 24-year-old.

Hickenlooper has crushed Romanoff in public polls and has bested him in recent fundraising, thanks in part to support from the Democratic Senatorial Campaign Committee. The official campaign arm for Senate Democrats has endorsed Hickenlooper’s bid to challenge Republican incumbent Sen. Cory Garder in 2020. According to the latest campaign finance reports, the former governor raised five times as much as Romanoff in the last quarter.

But Weindling thinks her group’s endorsement could turn the tide. For evidence, she points to what Sunrise has accomplished in just a few years.

Sunrise Coordinator Michele Weindling meets with Andrew Romanoff. The group is endorsing the former state House Speaker in the U.S. Senate race.

Since it formed in 2017, the group of politically savvy twenty-somethings helped elect Alexandria Ocasio-Cortez to the U.S. House. More recently, it has used sit-ins, protests and viral social media moments to help force the Green New Deal into the national conversation on climate change. Almost every Democratic presidential candidate has signed its pledge not to take big contributions from the fossil fuel industry.

The group also brings financial resources to the race. According to reporting by Inside Philanthropy, Sunrise raised $1 million in 2018 and plans to raise $2.5 million this year between both is 501(c)3 and 501(c)4 branches. In its 2018 budget, individual donors provided 35 percent of its funds and institutional funders providing 55 percent, including considerable support from the Rockefeller Family Fund and the Wallace Global Fund.

For 2020, the Sunrise Movement plans to make endorsements in several Democratic primary races, according to Political Director Evan Weber. The group is currently evaluating candidates in Maine, Georgia, Iowa and other potential must-win states for Democrats in their quest to retake the Senate. Sunrise plans to roll out more endorsements in the coming weeks.

Sunrise kicked off its latest series of endorsements in Colorado because members feared Hickenlooper, with his name recognition and popularity, could quickly outpace his Democratic rivals. Weber said local organizers decided on Romanoff after evaluating his platform and strengths as a candidate.

“They determined that Romanoff has a bold record and platform that aligns with our values — and the best chance of being someone who can take on both John Hickenlooper and Cory Gardner,” Weber said.

Hickenlooper has riled Sunrise members because, as governor, he resisted numerous voter-led efforts to limit the oil and gas industry in Colorado. Also, during his earlier short-lived presidential campaign, he signed the group’s No Fossil Fuel Money pledge, then backed out after realizing it banned donations from company executives.

As a presidential candidate, he also wrote an op-ed criticizing parts of the Green New Deal. Sunrise members say the position could hurt him during the Senate primary, pointing to a 2019 poll by Data for Progress, a left-wing think tank, that found 60 percent of likely Colorado voters support the platform.