Joe Biden’s lead rose among Democratic presidential contenders while Kamala Harris sank like a stone in a new poll released Tuesday, which also showed the other top four candidates essentially treading water.

The former veep — despite a series of characteristic gaffes in recent weeks — was the choice of 29 percent of those surveyed by CNN between Thursday and Sunday, up from 22 percent in a June survey by the cable network.

White House counselor Kellyanne Conway was quick to mock Harris, who is of Indian and Jamaican descent, for her falling numbers on Twitter, suggesting that Democrats were “racist and sexist” for not supporting her.

“Kamala Harris plummeted 12 points from June to August, according to a new @CNN #poll of Democrats about 2020. Using their own logic and lexicon, doesn’t that make Democrat primary voters ‘racist’ and ‘sexist’?” she wrote.

Team Trump has responded to charges of racism against the president over his immigration policies and attacks on a handful of minority lawmakers by accusing Democrats of branding anyone who disagrees with their policies as racists.

Harris, the California senator whose numbers rose after the first presidential debate, fell back to earth, garnering just 5 percent in the new poll compared to 17 percent in June.

The poll also showed that Bernie Sanders rose to 15 percent from 14 percent; Elizabeth Warren dropped from 15 percent to 14 percent while South Bend Mayor Pete Buttigieg rose a point to 5 percent.

None of the other candidates, including Beto O’Rourke, Julian Castro or Cory Booker, topped 3 percent.

New York’s entrants in the crowded field, Mayor de Blasio and Sen. Kirsten Gillibrand, each failed to crack 1 percent.

Biden’s jump in the poll comes as Democrats worry about his uneven performance in the debates and on the campaign trail, including a statement that suggested that minority children could be as smart as white children.

Harris’ post-debate surge came after she schooled Biden for his opposition to busing, leaving him flat-footed and without an effective comeback.

His staffers insist the gaffes are not a big problem, and are just “Joe being Joe.”

According to CNN, the sample of 1,001 voters included 28 percent who described themselves as Democrats, 26 percent who described themselves as Republicans and 46 percent who described themselves as independents or members of another party.

Results for the full sample have a margin of sampling error of plus or minus 3.7 percentage points. For the sub-sample of 402 Democrats and Democratic-leaning independents who are registered to vote and were asked about the primary candidates, it is 6.1 points.