Sen. Elizabeth Warren has vaulted to a 7-point lead over former Vice President Joe Biden in the Democratic primary race, according to a poll from Quinnipiac University released Thursday.

When asked whom they would vote for if the primary election were today, 28% of Democratic voters and independent voters who lean Democrat named the senator from Massachusetts, compared with 21% who selected Biden. Sen. Bernie Sanders of Vermont was third at 15%, and South Bend, Indiana, Mayor Pete Buttigieg finished fourth at 10%.

It was the fourth consecutive Quinnipiac poll in which Warren came out ahead of Biden. Before September, Biden consistently led Warren in Quinnipiac's surveys, usually by more than 10 percentage points.

But the poll appears to be an outlier compared with other recent surveys on the race.

Warren surged in late September and early October to drop Biden from the lead in the RealClearPolitics polling average for the first time since the race began. Since then, however, Biden has roared back, coming out ahead in every major national poll released after Oct. 15 except for Thursday's from Quinnipiac. One poll from CNN on Wednesday had the former vice president leading Warren by 15 percentage points.

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When asked who had the best policy ideas, Warren was the pick of 30% of likely Democratic voters, compared with Sanders at 20% and Biden at 15%, according to the Quinnipiac poll. But 28% felt Biden would make the best leader – 24% said Warren and 13% said Sanders – and he continued to lead in the all-important question of who is most likely to beat President Donald Trump.

Democratic voters have made it clear that the ability to defeat Trump is one of the most important factors in their 2020 primary decision. Biden has consistently been seen as the best positioned to unseat the president, but the percentage of Democratic voters saying that has slipped from a high of 56% in April to 42% now. The share of voters saying Warren is the one to beat Trump has gone from 3% in April to 20%.

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Warren came under fire from her rivals this month at the fourth Democratic presidential debate, getting hit particularly hard on the question of how she would pay for her health care plan. But 26% said she did the best job at the debate, compared with 17% who said Buttigieg was the winner, 12% who said it was Biden and 11% who said Sanders.

When asked who performed worst at the debate, Biden was the top pick at 15%. Eleven percent said Rep. Tulsi Gabbard, D-Hawaii, performed the worst.

"Last week's debate didn't help Vice President Joe Biden, who saw his numbers slip to where they were in early July following the first Democratic debate. Then, like now, he ranked among candidates doing the worst job in the debate. Later in July, his numbers rebounded. The question remains whether this is a blip or a trend," said Quinnipiac University polling analyst Mary Snow.