Former Vice President Joe Biden's lead in the race for the 2020 Democratic presidential nomination has shrunk by 10 percentage points in a CNN poll conducted since last week's debates that showed Kamala Harris and Elizabeth Warren getting significant bumps in support.

The poll of Democrats and Democratic-leaning independents found Biden drew support from 22 percent, compared with 32 percent a month ago, while Harris and Warren, who both delivered strong performances in the debate, drew 17 percent and 15 percent, respectively. Bernie Sanders had support of 14 percent of the Democrats surveyed, which is a 4 percentage point drop from the last CNN poll.

No other candidate got more than 5 percent support and the other Democratic hopefuls did not see a significant change after the two night of debates last week, the poll found.

Among those who followed news coverage of the debates, 41 percent said Harris did the best job, 13 percent said Warren was the standout, and 10 percent singled out Biden. Among those who said they watched at least one night of the debates, 46 percent said Harris did the best, 19 percent Warren, and 8 percent said Biden.

The debates featured 10 candidates each night. Warren appeared on the first night while Biden, Harris and Sanders were on stage for the second debate. Harris put Biden on the defensive when she confronted him his stance in opposition of busing to integrate schools.

The network surveyed 656 Democrats June 28-30 as part of a larger poll of voters in both parties. The Democratic portion of the poll had a margin of error of plus or minus 4.7 percentage points.