The Colorado Democrat who raised the most money in the battle to take on Republican Sen. Cory Gardner bowed out Tuesday, less than two weeks after former Gov. John Hickenlooper entered the primary.

Mike Johnston, a former state senator, said winning the primary would have been “an expensive and negative campaign” that went against his values.

Hickenlooper launched his bid for the Senate on Aug. 22, about a week after he suspended his campaign for president. National Democratic leaders had urged Hickenlooper to challenge Gardner, one of the most vulnerable Republican senators on the ballot in 2020. 

[Hickenlooper enters Colorado Senate race, but he will have competition]

Johnston, who ran unsuccessfully for governor in 2018, had raised $3.4 million for his Senate campaign, more than the $3.1 million Hickenlooper raised for his presidential run.

“I cannot be true to my values and lead a campaign that abandons the politics of what is possible in favor of a politics of attack, or a campaign that puts at risk the very goal my family entered this race to accomplish,” Johnston said in a statement. 

Hickenlooper picked up several high-profile endorsements after entering the race — including from the Democratic Senatorial Campaign Committee — and recent polling has shown him ahead in both the Democratic primary and against Gardner. 

He still faces several challengers for the Democratic nomination, and will have to address statements he made earlier this year that he was not interested in being a senator. 

Colorado will be one of the top Senate battlegrounds next year. Before Hickenlooper’s announcement, Inside Elections with Nathan L. Gonzales rated the race a “Toss-up.”

There are still 11 candidates vying for the Democratic nomination, Denver’s Fox31 News reported.