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For the first time in his two-cycle pursuit of the Democratic presidential nomination — and at about the best time for such a peak — U.S. Sen. Bernie Sanders leads the Des Moines Register/CNN/Mediacom Iowa Poll.

The senator from Vermont is the top choice of 20% of likely Democratic caucusgoers, according to the poll by Selzer & Co. That places him 3 percentage points ahead of Elizabeth Warren, 4 points ahead of Pete Buttigieg and 5 points ahead of Joe Biden. No other candidate has double-digit support.

This poll also brings his highest favorability rating since June — 66% of likely Democratic caucusgoers have favorable feelings toward him, versus 29% with unfavorable feelings. That's an 11-point increase in net favorability since the November Iowa Poll.

He keeps his locked-in, enthusiastic base of support — a clear advantage over the other leading candidates: 49% of his supporters say they’re extremely enthusiastic to caucus for him — 17 percentage points higher than the share for his closest rival, Warren.

And, in what pollster J. Ann Selzer calls his best number of the poll, 59% of his supporters say their mind is made up. Warren is once again next, at 48%.

“For real, he could win the caucuses,” Selzer said. “His supporters are more committed and more entrenched.”

The poll, conducted Jan. 2-8, surveyed 701 likely Democratic caucusgoers and has a margin of error of plus or minus 3.7 percentage points.

His peaks come with valleys, however. He leads the other top-tier candidates in support among people younger than 35, at 36%. But he has just 5% support among likely Democratic caucusgoers 65 or older.

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His support also divides along economic and education fault lines. He leads the field in support from those with less than a college degree, 29%, compared to 14% from those with college degrees or higher. His support registers at 28% among those with incomes under $70,000, but just 15 percent among those earning $70,000 or more.

Another cautionary sign: Buttigieg and Warren have larger "footprints," adding together those who name each of them as their first or second choice or are actively considering them. That means he has less room to add supporters.

“He’s more polarizing,” Selzer said. “So it will be up to campaign staff to get his people to show on caucus night in order to turn his potential into reality, come February.”

More coverage on the Iowa Poll:

Jackie Moore, 31, a poll respondent from Coralville, said her generation grew up in the shadow of the Sept. 11 attacks, and, if they didn’t come of age during the Great Recession, they entered a working world shaped by it.

"I, personally, graduated at the height of the economic crisis,” she said. “Not being able to find a full-time job for two to three years after that really made me think deeply about issues affecting not only me, but everyone around me."

The country’s heightening partisan divide also reduces her interest in more centrist candidates.

“At this point, I think our country is so divided between left and right I don't think a centrist will make that much of a difference,” Moore said. “So we might as well lean far left, and hope to get things we really need, instead of lean center and hope things are less hostile."

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About this poll

The Iowa Poll, conducted Jan. 2-8, 2020, for the Des Moines Register, CNN and Mediacom by Selzer & Co. of Des Moines, is based on telephone interviews with 3,131 registered voters in Iowa, including 701 who say they will definitely or probably attend the 2020 Democratic caucuses.

Interviewers with Quantel Research contacted randomly selected active voters from the Iowa secretary of state’s voter registration list by telephone. The sample was supplemented with additional phone number lookups. Interviews were administered in English. Responses for all registered voters were adjusted by age and congressional district to reflect their proportions among active voters in the list.

Questions based on the sample of 701 voters likely to attend the 2020 Iowa Democratic caucuses have a maximum margin of error of plus or minus 3.7 percentage points. Questions based on the sample of 3,131 registered voters have a maximum margin of error of plus or minus 1.8 percentage points. This means that if this survey were repeated using the same questions and the same methodology, 19 times out of 20, the findings would not vary from the true population value by more than plus or minus 3.7 or 1.8 percentage points, respectively. Results based on smaller samples of respondents — such as by gender or age — have a larger margin of error.

Republishing the copyright Iowa Poll without credit to the Des Moines Register, CNN, and Mediacom is prohibited.

► MORE ON THIS POLL: Read our methodology

Nick Coltrain is a politics and data reporter for the Register. Reach him at ncoltrain@registermedia.com or at 515-284-8361.