Bernie Sanders holds a 12-point lead over Elizabeth Warren in Colorado's crowded Democratic presidential primary race just days before ballots are due, according to a new survey released Thursday by Louisville-based Republican polling firm Magellan Strategies.

Sanders, who won Colorado' caucuses four years ago with 60% of the vote, tops the field of eight major Democrats, with 27% of likely primary voters picking the Vermont senator in the telephone survey, which was conducted Monday and Tuesday.

Massachusetts senator Warren follows with 15%, and the next three candidates are tightly bunched, with former South Bend, Indiana, Mayor Pete Buttigieg in third with 12%, followed by former New York Mayor Mike Bloomberg and former Vice President Joe Biden tied for fourth place, each with 11% support.

Minnesota Sen. Amy Klobuchar has 6% support, with California investor Tom Steyer and Hawaii Rep. Tulsi Gabbard bringing up the rear, with 1% support apiece.

The pollster used live interviewers to contact 500 likely primary voters on landlines and cell phones on Feb. 24 and 25. The survey has a margin of error of 4.38%. Read the full poll results here.

Colorado voters have been returning mail ballots for two weeks ahead of the state's March 3 presidential primary. This year, it falls on Super Tuesday, when 14 other states and territories cast ballots in the Democratic primary, awarding roughly one-third of the pledged delegates to the national convention.

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Sanders has led national polls in recent weeks and notched wins in the first three nominating contests, though he finished in a virtual tie with Buttigieg in the Iowa caucuses.

With Sanders out front in Colorado by a wide margin and the next four candidates all within the margin of error of the 15% threshold needed to win delegates, pollster David Flaherty said the 13% of undecided voters "will be pivotal in determining the final outcome."

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Candidates are allotted delegates to the Democratic National Convention in Milwaukee if they break 15% statewide or in any of Colorado's seven congressional districts.

"Right now," Flaherty said, "the 12-point lead for Sanders means that he is the only candidate who can feel optimistic about his chances in Colorado on Super Tuesday."

A clear majority of Colorado's Democratic primary voters say it's most important to pick a candidate who can defeat Trump in November over a candidate who shares the voter's values and personal beliefs, the poll found.

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Fully 57% say they prioritize electability, while 36% say agreeing with a candidate's values is most important.

Beating Trump is considered most important by higher numbers of voters over age 45, moderates, women and registered Democrats, as opposed to unaffiliated voters. A majority of voters younger than 45, however, say shared values and beliefs is more important than winning the general election, by a 9-point margin.

Nearly all the presidential candidates have campaigned in Colorado in recent weeks, with large rallies held by Sanders, Trump, Buttigieg and Warren.

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According to the Magellan poll, Sanders holds a 29-point lead among voters younger than 45 and a 21-point lead among voters who describe themselves as very liberal. Among self-described moderates, Sanders is in a virtual tie with Buttigieg and Bloomberg, with 18% support to their 17%.

Voters age 65 and older prefer Bloomberg, who has 19% support, and Biden, at 18%, over the 15% for Sanders.

In the 45-64 age group, Buttigieg and Sanders are tied for the lead with 20% each, followed closely by Warren with 18%. (The pollster cautions against drawing any firm conclusions from the candidates' performances in the subgroups, because the margin of error soars compared to the poll's sample as a whole.)

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The results of the Magellan survey are similar to a Colorado Democratic primary poll released Wednesday by Data For Progress, a left-leaning organization that says it uses "state-of-the-art techniques in data science to support progressive activists and causes."

That poll found Sanders leading Warren by 14 points, 34% to 20%, with Buttigieg and Bloomberg tied for third place with 14% each, followed by Biden at 10% support. None of the other candidates had support in the double digits. The survey's margin of error was 4.7%.