Former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE leads the field of Democratic presidential hopefuls by double digits a month ahead of the Iowa caucuses, according to a Harvard CAPS/Harris poll released exclusively to The Hill.

The poll shows Biden registering 30 percent support among Democrats nationally. In a relatively distant second place is Sen. Bernie Sanders Bernie SandersSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Schumer, Sanders call for Senate panel to address election security MORE (I-Vt.), who notched 17 percent in the survey.

Sen. Elizabeth Warren Elizabeth WarrenNo new taxes for the ultra rich — fix bad tax policy instead Democrats back away from quick reversal of Trump tax cuts It's time for newspapers to stop endorsing presidential candidates MORE (D-Mass.) is lingering in the No. 3 spot with 12 percent support. No other candidate registered double-digit support. Former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq A socially and environmentally just way to fight climate change MORE came in fourth place at 7 percent, while former tech executive Andrew Yang Andrew YangDoctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls Buttigieg launches his own podcast MORE notched 3 percent support.

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“Biden continues to be the front-runner but the surprise is really the growth of Sanders while Warren has shrunk,” said Mark Penn Mark PennThe 7 keys to victory in the presidential race Biden leads Trump on law and order, coronavirus: poll Majority expect to see coronavirus vaccine in 2021: poll MORE, the co-director of the Harvard CAPS/Harris poll. “Just a few months ago this was a Warren race — today it’s more likely to come down to Biden vs. Sanders.”

The poll shows little change from a previous Harvard CAPS/Harris survey conducted in late November that put Biden at 29 percent, Sanders at 16 percent, Warren at 13 percent and Buttigieg at 8 percent, suggesting that the state of the race may be steadying even before the first votes are cast next month.

Still, recent polls in early primary and caucus states show a more fluid race.

An Emerson College survey of likely Iowa Democratic caucusgoers released last month showed Biden and Sanders in a statistical tie for first place, with 23 percent and 22 percent support, respectively.

And a WBUR-MassINC poll of New Hampshire Democrats from December showed Buttigieg and Biden knotted at the top with 18 percent and 17 percent, respectively. Sanders wasn’t far behind in that survey, with 15 percent support.

The Harvard CAPS/Harris Poll survey was conducted online within the U.S. among a representative sample of 780 registered Democratic voters between Dec. 27-29 by the Harris Poll.

Results were weighted for age within gender, region, race/ethnicity, marital status, household size, income, employment, education, political party, and political ideology where necessary to align them with their actual proportions in the population. Propensity score weighting was also used to adjust for respondents’ propensity to be online.