A new national poll suggests a three-way tie between Sen. Bernie Sanders of Vermont, Sen. Elizabeth Warren of Massachusetts and former Vice President Joe Biden in the race for the Democratic presidential nomination.

And the survey – released Monday by Monmouth University – indicates a massive drop for Biden, the front-runner in the nomination race since before he declared his candidacy in late April. It also reflects an increase in support for both Sanders and Warren, the Democratic Party’s two progressive standard-bearers.

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Sanders and Warren are both at 20 percent in the poll, with Biden at 19 percent. The former vice president plunged 13 percentage points from the 32 percent he stood in June in Monmouth’s last national poll on the Democratic nomination race. Sanders rose six points from the June poll, with Warren rising five points.

The Biden campaign took aim at the survey, telling reporters "this poll is an outlier that is contradicted by every measure of the national average."

The campaign pointed to the Real Clear Politics average of the latest national polls in the 2020 Democratic nomination race, which indicate Biden holds a double digit lead over Sanders and Warren, his two closest competitors.

“The main takeaway from this poll is that the Democratic race has become volatile,” Monmouth University Polling Institute director Patrick Murray said.

“Liberal voters are starting to cast about for a candidate they can identify with," Murray said. "Moderate voters, who have been paying less attention, seem to be expressing doubts about Biden. But they are swinging more toward one of the left-leaning contenders with high name recognition rather than toward a lesser-known candidate who might be more in line with them politically."

The poll suggests Biden “suffered an across the board decline” with a 14-point drop from June to August with white Democrats, a 17-point free-fall among voters without a college degree, a 14-point plunge among men, a 13-point drop among women, and a nine-point deterioration among voters 50 and older. He also went from 40 percent in June to 22 percent now among Democrats who consider themselves moderate or conservative.

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Most of Biden’s lost support in those groups shifted almost equally to Sanders and Warren.

Sen. Kamala Harris of California is a distant fourth in the Monmouth Poll, at 8 percent, with Sen. Cory Booker of New Jersey and South Bend, Indiana Mayor Pete Buttigieg both at 4 percent. Entrepreneur Andrew York is at 3 percent, with former Rep. Beto O’Rourke of Texas, former Housing and Urban Development Secretary Julian Castro and best-selling spiritual author Marianne Williamson each at 2 percent. Everyone else questioned in the poll registered at 1 percent or less.

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The Monmouth University Poll was conducted Aug. 16-20, with 800 adults nationwide questioned by live telephone operators. Results for the Democratic presidential nomination race were based on 298 registered voters who identified as Democrats or leaned towards the Democratic Party – and have a sampling error of plus or minus 5.7 percentage points.