New polling of likely Colorado voters released Sept. 3 shows former Gov. John Hickenlooper opening up a lead over U.S. Sen. Cory Gardner on the strength of a wide advantage among unaffiliated voters just weeks before ballots are set to go out.

The survey, conducted online Aug. 21-30 by Morning Consult, found the Republican incumbent trailing his Democratic challenger by 9 percentage points, 48% to 39%.

While both candidates have solid support from fellow partisans, Hickenlooper holds a 29 percentage point lead with Coloradans registered unaffiliated or with third parties, who make up more 40% of the state's registered voters.

The poll found former Vice President Joe Biden with a 10 percentage point lead over President Donald Trump among likely Colorado voters, with 51% support to the incumbent's 41%. Biden led the independent group of voters by 25 percentage points.

Hickenlooper's lead in the tracking survey has widened since polling released a month ago by the same firm showed the Democrat with a 6 percentage point edge, 48% to 42%. Biden led Trump by 13 percentage points in the July poll.

Gardner, considered among the most vulnerable Republican senators on the ballot this year, "has a math problem," Morning Consult's Eli Yokley wrote in an analysis of the data.

“The unaffiliated voters are all that matter, especially in a hyperpolarized environment where you can count on your base to show up,” Ryan Winger, director of data analysis and research projects at the Louisville-based Republican polling firm Magellan Strategies, told Yokley.

According to the poll, Hickenlooper counts the support of 91% of registered Democrats, who make up about 30% of the state's voters, while Gardner has the support of 88% of Republicans, who account for 27% of voters.

It's Hickenlooper's wide 54%-to-25% lead among voters who aren't registered with either major party that spells trouble for Gardner, who is seeking a second term.

The poll also found that 3% of likely Republican voters support Hickenlooper and 4% of likely Republican voters support Biden, while Gardner and Trump didn't register any support from Democrats.

The poll surveyed 638 likely voters and has a margin of error of plus or minus 4 percentage points.

Hickenlooper has led Gardner by varying margins in every public poll released this year, according to the political number-crunchers at FiveThirtyEight. Colorado has tilted increasingly toward the Democrats in recent elections, including the party nearly sweeping the ballot last cycle, when not a single Republican was elected statewide and Democrats took control of the state Senate while increasing the margin in the state House.

Aurora Mayor Mike Coffman, the Republican who lost a 2018 bid for a sixth term, suggested that perceptions Trump could lose might benefit Gardner by encouraging ticket-splitters to vote for a GOP senator to keep a check on Biden.

“I won in 2016 with Trump on the ballot, and the reason I did was because there was a general belief that Trump couldn’t win and that they needed a balance with a Republican-controlled Congress versus Democrat Hillary Clinton in the White House,” Coffman told Yokely.

This story is from Colorado Politics, a statewide political and public policy news journal. Used by permission. For more, visit coloradopolitics.com.