Alice Madden on Friday became the fourth high-profile Democrat to quit Colorado’s U.S. Senate primary, saying she doubted she had a “realistic path to victory” after former Colorado Gov. John Hickenlooper joined the field hoping to unseat Republican U.S. Sen. Cory Gardner.

The former state House majority leader from Boulder said in a statement that “[t]he dire need to forge solutions to the climate crisis” led her to run against Gardner, adding that she intends to “do my best to ensure we keep the need for decisive action at the forefront of this Senate contest and beyond.”

Madden’s withdrawal follows the departures of former state Sen. Mike Johnston, former U.S. Attorney for Colorado John Walsh and former Obama-era ambassador Dan Baer, who ended their campaigns within weeks of Hickenlooper’s declaration in late August that he was jumping in the crowded primary after ending his presidential bid.

Last weekend, Madden telegraphed her impending exit from the primary in an interview with the Washington Post’s Dave Weigel, who was in Colorado to report on the Senate race.

Madden told Weigel that she’d anticipated reaching out to “progressives, to women, to environmental groups, to unions,” but the wind went out of her sails once the popular former two-term governor declared his candidacy.

“Hickenlooper getting in has had the effect of them all saying, ‘Well, gosh, maybe we’ll just wait and see what happens,'” Madden said. “And the longer people delay on endorsing, the more the momentum behind him is seemingly inevitable.”

Madden’s decision to drop out was first reported by Colorado Independent columnist Mike Littwin.

The former director of a clean energy center at the University of Colorado and official in the U.S. Department of Energy during the Obama administration said Friday that she was encouraged by the recent sense of urgency surrounding the climate.

“I was proud to march with the thousands of Coloradans at the climate strike and today we see thousands more gather to see Greta Thunberg – people of all ages, incomes and backgrounds – demanding transformative change,” Madden said in a release, referring to the 16-year-old Swedish activist who was leading a “climate strike” in downtown Denver on Friday.

“As disappointing [as] it is to leave this race, they give me hope,” Madden said. “The clarion call to our elected officials is loud and clear. Together, we can lead this country to a carbon net-negative future, including an inclusive clean energy economy that helps expand our middle class.”

In addition to Hickenlooper, eight Democrats remain in the primary, including former state House Speaker Andrew Romanoff, state Sen. Angela Williams, former congressional candidate Stephany Rose Spaulding and several candidates who are making their first run for office.