WASHINGTON – The fight for the Democratic presidential nomination remains in flux as voters in early states prepare to cast the first ballots in the race next month, according to a pair of national polls released Wednesday.

Sen. Bernie Sanders, I-Vt., surged into first place in a CNN poll conducted by SSRS, marking the first time a CNN poll did not find former vice president Joe Biden alone at the head of the field since the race began.

The CNN poll found Sanders was the choice of 27% of registered Democrats and Democratic-leaning independents, compared with 24% who preferred Biden. That represented a seven-point leap ahead for Sanders and a two-point drop for Biden from CNN's poll in December.

Sen. Elizabeth Warren of Massachusetts was third at 14% (down two percentage points from the month before) and former South Bend, Indiana, Mayor Pete Buttigieg was fourth at 11% (up three percentage points from December). Former New York City Mayor Michael Bloomberg came in at 5%, and Sen. Amy Klobuchar of Minnesota tied entrepreneur Andrew Yang at 4%. The rest of the field had 2% or less support.

A poll from Monmouth University, however, found Biden not only still had the lead at 30% but appeared to be gaining momentum since falling out of first place in Monmouth University national polling in August.

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That month he finished one percentage point behind Warren and Sanders, who tied at 20%. Warren briefly held first place by herself in Monmouth's September poll at 28%, but by November Biden had tied her at the top. And in December, the former vice president was again in the lead at 26%, while Sanders had climbed into second.

Sanders was again in second behind Biden in Wednesday's poll, which found him as the choice of 23% of Democratic and Democratic-leaning voters. Warren was in third at 14%, followed by Bloomberg at 9%, Buttigieg at 6%, Klobuchar at 5%, Yang at 3% and the rest of the pack at 1% or less.

"With the exception of Bloomberg’s entry, this race looks pretty much like it did six months ago," Monmouth University Polling Institute director Patrick Murray said. "But that stability masks the potential for sizable swings once the first contests are held. Iowa and New Hampshire will play a major role in shaping national voter preferences."

It may not take much to sway some voters. The CNN poll found 58% registered Democrats and Democratic-leaning independents still think they might change their mind, while 42% say they will "definitely" vote for their chosen candidate.

Those voters positions appearing to be softening rather than hardening as the time to vote approaches. In November, 47% said they definitely planned to vote for their candidate, while 52% said they were still open to switching their support. By comparison, only 37% told CNN they might still change their mind at this point in 2016.

Sanders' support in the CNN poll is surprising given that 57% of Democratic primary and caucus voters say the most important thing is that the nominee can beat Trump, while 35% say what matters is whether they agree with the candidate on all the issues. Forty-five percent thought Biden had the best chance to beat Trump, compared with 24% who said Sanders does. But more (30%) said Sanders agrees with them on the issues that matter most

The CNN poll found every top Democratic candidate would beat Trump in a hypothetical matchup. Here's how those broke down:

Biden 53%, Trump 44%

Sanders 52%, Trump 45%

Warren 50%, Trump 45%

Bloomberg 52%, Trump 43%

Buttigieg 49%, Trump 45%

Klobuchar 48%, Trump 45%

The Monmouth poll found that Democratic voters are not happy with the current calendar for their party's primaries and caucuses. Fifty-eight percent said they would prefer a national primary, while just 11% favored keeping the current system.

The CNN poll was conducted Jan. 16-19 with a margin of error of plus or minus 3.4 percentage points. The margin of error for Democratic voters and Democratic-leaning independents was 5.3 percentage points.

The Monmouth University poll was conducted Jan. 16-20 with a margin of error of plus or minus 3.4 percentage points overall and a margin of error of plus or minus 5.1 percentage points among Democratic voters and Democratic-leaning independents.