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.

Likely caucusgoers continued to be divided along two key lines in assessing their choices for president: age and ideology. Among those under age 45, Sanders has a 9-point edge over Biden, 32% to 23%, with Warren at 10% and Harris at 9%. Among older likely caucusgoers, Biden stands 15 points ahead of Sanders, 32% to 17%, with no other candidate in double digits.

The ideological divide is similar. Among liberals, 30% back Sanders, 21% Biden, 11% Warren and 7% each Harris and O'Rourke. Moderate or conservative likely caucusgoers, however, give Biden a wide edge: 36% to Sanders' 18%, with the rest below 10%.

The CNN/Des Moines Register/Mediacom poll was conducted by Selzer & Co. of Des Moines, Iowa, from last Sunday through Wednesday among a random sample of 401 likely Democratic caucusgoers reached on landlines or cell phones by a live interviewer. Results for the sample of likely caucusgoers have a margin of sampling error of plus or minus 4.9 percentage points; it is larger for subgroups.