The poll marks the first time Biden has not held a solo lead in CNN's national polling on the race.

Overall, 27% of registered voters who are Democrats or Democratic-leaning independents back Sanders, while 24% favor Biden. The margin between the two is within the poll's margin of sampling error, meaning there is no clear leader in this poll. Both, however, are significantly ahead of the rest of the field, including Massachusetts Sen. Elizabeth Warren at 14% and former South Bend, Indiana, Mayor Pete Buttigieg at 11%. Former New York Mayor Michael Bloomberg lands at 5% in the poll, while Minnesota Sen. Amy Klobuchar and businessman Andrew Yang each hold 4% support. Businessman Tom Steyer has 2%. No other candidate reaches 1% support.

Sanders has gained 7 points since the last CNN poll on the race in December. Since that survey, the Vermont senator has also made gains in early-state polling, including CNN's survey with the Des Moines Register in Iowa, where the first caucuses of the cycle will be held in less than two weeks.

Sanders has made gains nearly across the board, clearly pulling away from Warren among liberals (33% back Sanders, while 19% support Warren in the new poll), a group where the two had been running closely through much of the fall. Sanders has also pulled about even with Biden among voters of color (30% for Sanders, 27% for Biden).

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