Former Colorado state Sen. Mike Johnston (D) ended his senate bid Tuesday, becoming the first Democrat to drop out since former Gov. John Hickenlooper John HickenlooperThe Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Cook Political Report shifts Colorado Senate race toward Democrat Willie Nelson playing at virtual fundraiser for Hickenlooper MORE (D) announced his campaign.

“As we looked out at the road ahead, what I saw is to win this Democratic primary would now require an expensive and a negative campaign. And that’s not who I am,” he told The Colorado Sun. “I think no race is worth conceding victory to a brand of broken politics that I’ve spent my life trying to change.”

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Johnston specifically cited Hickenlooper’s entry into the crowded Senate primary, telling the Sun that he would only be able to win the Democratic nomination by spending money and time attacking the former governor, a move he fears could help endangered incumbent Sen. Cory Gardner Cory Scott GardnerBreaking the Chinese space addiction Trump dumbfounds GOP with latest unforced error Billionaire who donated to Trump in 2016 donates to Biden MORE (R) in the general race.

“I don’t think that is good for us, or good for the country, or good for the nominee,” he said. “For me with the climate crisis and the future of the Supreme Court and the core tenets of democracy on the line, I just couldn’t take that risk.”

Johnston, who unsuccessfully ran for governor last year and was one of the top fundraisers in the Senate race, added that he has not yet made a decision about an endorsement or what he intends to do with the millions left in his campaign account.

His withdrawal shows how Hickenlooper’s entry into the race could shake up the primary race.

Banking on Hickenlooper’s existing power structure in the Centennial State from his time as its chief executive, the Democratic Senatorial Campaign Committee was quick to throw its support behind Hickenlooper, telling The Hill that he is “far and away the strongest candidate to beat Cory Gardner, and we’re proud to support him in his run for Senate.”

But despite the establishment groundswell behind Hickenlooper, several progressive candidates in the race vowed they would not stop campaigning and hammered the former governor for the moderate positions he took in his short-lived presidential bid.

"During his short-lived presidential campaign, Governor Hickenlooper ran hard against the strong progressive energy in our party right now, and away from the big, bold, progressive solutions that our state and our country need. After spending the first half of this year campaigning against progressive ideas, he has some serious explaining to do to Colorado voters," state Sen. Angela Williams wrote in an op-ed for The Sentinel.

“We need leaders who are not conditioned by a lifetime in politics to be afraid of anything more than incremental change. That means we need different types of leaders. ... We can mend the country and win our future. We need ethical, bold, progressive leadership in Washington," added former U.S. Ambassador Dan Baer.

The Democratic Party has high hopes for the Colorado Senate race, viewing Gardner as particularly vulnerable in a state Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE won in 2016. The Cook Political Report, a nonpartisan election handicapper, rates the race as a “toss up.”