Sanders support advanced to 32% among Democrats and Democratic-leaning independents. It is eight percentage points more than the last poll from late January.
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Biden trails with 17% support, followed closely by former New York City Mayor Michael Bloomberg at 14%.
Massachusetts Sen. Elizabeth Warren is in fourth place at 11%.
Despite strong performances in Iowa and New Hampshire, Pete Buttigieg is in the single digits at 7%.
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Minnesota Sen. Amy Klobuchar, who finished third in the New Hampshire primary, is at 6%.
The new numbers come as Bloomberg qualified for his first Democratic presidential debate. He won't be on the ballot for Nevada's caucuses this Saturday. He is skipping the first four contests and instead focusing on performing well on Super Tuesday on March 3.
Sanders, Biden, Bloomberg, Warren, Buttigieg, Klobuchar will face off in a debate Wednesday.
ABC News contributed to this report.