A new survey of Democratic voters found that former Vice President Joe Biden and Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts are all statistically tied for first place in their party's presidential primary.

Monmouth University released the poll Monday afternoon, which found Sanders and Warren both currently receiving 20 points and Biden receiving 19 points. The poll was particularly damaging for Biden, who dropped 13 points since the university did its last poll in June.

Sanders, on the other hand, gained 6 points, whereas Warren improved her numbers by 5 points.

The numbers should be treated with caution because Monmouth said the poll has a 5.7 percentage point sampling margin of error.

California Sen. Kamala Harris remained stable at 8%, while New Jersey Sen. Cory Booker's support doubled, from 2% in June to 4%.

Other potentially troubling news for the former vice president was the fact that he found his favorability ratings drop 8 points to 66% from the last time the question was asked in May. Warren, however, found her favorability numbers rise 5% to 65%.

The poll also found that 10% of Democratic or Democratic-leaning voters are still undecided.

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