Democrat Jared Polis holds an 8-percentage-point advantage over Republican Walker Stapleton in the Colorado governor’s race, and an even wider advantage among people who already have voted, according to a poll from Colorado firms released Thursday.

The live telephone survey of 517 Colorado adults was conducted Oct. 25-30 by Telluride-based Keating Research Inc. and Denver-based OnSight Public Affairs along with Martin Campaigns. Keating and OnSight often work for Democrats running for office.

Fifty percent of those surveyed said they had voted for, or planned to vote for, Polis, while 42 percent said they support Stapleton, 4 percent back Libertarian Scott Helker, 1 percent favor Bill Hammons of the Unity Party, and 4 percent said they were undecided.

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The pollsters noted that of several public surveys conducted in the 2018 Colorado governor’s race since the June primary election, all of which showed an advantage for Polis, theirs is the first to show the Democrat with support at or above 50 percent, although that conclusion is within the latest survey’s margin of error.

Veteran pollster Chris Keating of Keating Research, in releasing the Keating-OnSight-Martin Colorado Poll’s results, all but declared the election for Polis, the Boulder congressman and internet entrepreneur.

“In 23 years of polling in Colorado, a statewide candidate with this type of consistent 7- to 8-point lead in the polls has never lost the election,” Keating said, referring to previous Polis-Stapleton poll results as well as his. “Our statistical model gives Jared Polis a 98 percent chance of winning.”

It also shows that the pool of undecided voters does not appear to be large enough to cover the spread between Polis and Stapleton, the state treasurer and businessman.

> RELATED: With Election Day approaching fast, Polis, Crow lead in polls

The poll comes as ballot returns so far show a higher voting rate by Democrats when compared to Colorado’s last midterm election in 2014.

A report accompanying the new poll says that while Republicans strongly support their party’s candidate – 87 percent for Stapleton versus 8 percent for Polis – Democrats also overwhelmingly support their candidate, and “the weak Republican turnout and robust unaffiliated voter support for Polis (53 percent vs. 32 percent for Stapleton) will drive Polis to victory on election night.”

The report also cites nearly 2-1 support for Polis in Arapahoe and Jefferson counties, two bellwether Denver-suburban counties “that tend to determine the outcome of Colorado elections.”

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The poll results show that 54 percent of those surveyed had already voted. Thirty percent of all likely voters surveyed said they had already voted for Polis, and 19 percent said they had already voted for Stapleton.

Twenty percent of the 517 people surveyed said they had not yet voted but planned to vote for Stapleton, while 18 percent said they planned to vote for Polis.

The poll also asked about support for President Donald Trump, whose presidency has been a major election issue in Colorado and across the nation.

Of those Coloradans surveyed, 39 percent said they have a favorable opinion of Trump, while 59 percent said they regard the president unfavorably.

At the extremes, 22 percent of poll respondents said they view Trump very favorably, but more than half – 52 percent – said they regard him very unfavorably.

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The poll found strong support for Colorado Gov. John Hickenlooper – a 59-to-33 percent favorability margin. The term-limited Democrat is leaving office in January and signaled Wednesday that he is strongly considering a 2020 run for the presidency.

“Hickenlooper has an eight-year track record of bringing Coloradans together,” said Curtis Hubbard, an OnSight partner and a former Denver Post editorial page editor. (Hickenlooper’s last gubernatorial campaign was a client of Hubbard’s firm.)

Surveyed Coloradans were more split on U.S. Sen. Cory Gardner, with 42 percent saying they view the Colorado Republican favorably and 43 percent with an unfavorable impression, while 16 percent said they don’t know one way or the other or are unfamiliar with Gardner. He is up for election in 2020.

Asked about their political affiliation, 40 percent of those surveyed said they think of themselves as independent, 30 percent call themselves Democrats, and 29 percent identify as Republicans. But as far as official party registration goes, the voters surveyed came down as 33 percent Democrat, 33 percent Republican and 33 percent unaffiliated.

The Keating-OnSight-Martin Colorado Poll has an estimated margin of error of plus or minus 4.3 percent. Live interviewers reached voters by phone: 61 percent on mobile phones and 39 percent via land lines.

Those surveyed were people who voted in November of 2014, 2016 and 2017 and who told pollsters they either already voted or planned to vote in the election that ends Nov. 6.

Neither Keating Research nor OnSight Public Affairs worked for Polis during this election cycle. They did work for his Democratic opponents before the primary.

The survey was one of two released Thursday. The other poll, from Republican firm Magellan Strategies, found a narrower, 5-point split among likely voters between the two candidates, with 45 percent favoring Polis and 40 percent for Stapleton. The Magellan survey also found a much larger pool of undecided voters: 11 percent of those polled.

But David Flaherty, Magellan Strategies CEO, told Ernest Luning of Colorado Politics that, given the trend of higher participation by Democrats this year than in previous midterm elections, “we completely understand that the final voter turnout by party may be less Republican than this survey indicates.”

Join us at ColoradoPolitics.com on election night, Tuesday, Nov. 6, for election results.