Washington (CNN) The field of Democrats seeking the party's nomination for president in 2020 is one of the largest the party has seen, but for Iowa's most likely caucus attendees, two names stand above the rest: former Vice President Joe Biden and Sen. Bernie Sanders of Vermont.

The latest CNN/Des Moines Register/Mediacom poll finds Biden and Sanders near even at 27% and 25% respectively, with no other candidate earning even 10% support. Sen. Elizabeth Warren of Massachusetts (9%) and Sen. Kamala Harris of California (7%) come closest, and of the rest of the 20-person field tested in the poll, just former US Rep. Beto O'Rourke of Texas (5%), Sen. Cory Booker of New Jersey and Sen. Amy Klobuchar of Minnesota (3% each) rise above 1% support.

The numbers haven't shifted dramatically since our December poll : Biden and Sanders were the top two then, though their relative position has tightened. While Biden led by 13 points in December, he and Sanders are about even now. And the flurry of energy behind O'Rourke following his narrower-than-expected loss to Sen. Ted Cruz in November seems to have dissipated some, with his numbers slipping 6 points in the last few months. For the rest of the field, though, things are about the same now as they were then.

Several candidates land below the 1% marker set out as a baseline for inclusion in the Democratic National Committee's upcoming debates -- including Sen. Kirsten Gillibrand of New York and former Colorado Gov. John Hickenlooper.

A handful of candidates have seen improvements in their favorability numbers since December, and nearly all of those had announced their candidacies in between the two polls. Harris leads the pack, with her favorability number climbing 9 points to 58% while her negatives held steady. Former Secretary of Housing and Urban Development Julian Castro's numbers have climbed 6 points (33% favorable now), as have Washington state Gov. Jay Inslee's (17% favorable in the new poll). Klobuchar's positive numbers have gone up 5 points to 43%. Klobuchar has seen a corresponding rise in negative views, however, with 15% now saying they have unfavorable opinions, up from 8% in December.

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