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Democratic White House frontrunner Joe Biden is creeping up in the polls but the gap between him and the remaining candidates is narrowing overall, according to an SSRS/CNN poll released on Tuesday.

In another dramatic twist of poll numbers, Democrat Kamala Harris, the U.S. senator from Oakland, dropped several percentage points, and one strategist blamed her attack on Biden at a July debate over his past stances on crime and his positive reflections about segregationist senators.

“We often see popular candidates get a bounce out of being attacked by less popular candidates,” pollster Ron Lester told Fortune.

“When you attack a candidate who is more popular than you, it’s very important to have a solid foundation and basis for the attack,” continued Lester, who is based in Washington. “Not only did Harris attack Biden but she also—by way of implication and directly—attacked Barack Obama, the most popular Democratic political figure in the country.“

It is important to note, however, that no matter how poll numbers are fluctuating in this pre-primary part of the campaign, the timing is still pretty far out from November 2020, Democratic strategist Kristen Hawn said.

“Biden, he has tendencies to have some of these gaps,” said Hawn, a senior adviser with the Rokk Solutions public affairs firm in Washington.

“I think generally what we’re seeing is the public finds him one of the most likely—if not the most likely—to beat Trump,” she said, noting as an example his lack of support for Medicare for all and recognition that some Americans fear losing employer-based health insurance. “Biden … is the one maintaining the middle ground, which is always the line you have to walk.”

The poll, conducted August 15-18 by landline and cellphone, asked 1,001 Democratic and Democratic-leaning likely voters who they would probably support in their primary.

Their responses:

Biden, 29%, compared to 22% in late June, but down from 39% in late April.
U.S. Sen. Bernie Sanders, D-Vermont, 15%, compared to 14% in late June and equal to the 15% he generated in late April.
U.S. Sen. Elizabeth Warren, D-Mass., 14%, compared to 15% in late June and up from 8% in late April.
South Bend, Ind., Mayor Pete Buttigieg, 5%, compared to 4% in late June and down from 7% in late April.
U.S. Sen. Kamala Harris, D-Calif., 5%, compared to 17% in late June and equal to the 5% she generated in late April.

Regarding her attacks on Biden at Democratic debates in Miami and Detroit, Lester said Harris took a bold gamble and lost, to the tune of 12 percentage points. The invisible guest at the table is former President Barack Obama, who Americans last year rated as the best president of their lifetimes.

“Obama is in a class by himself, especially among black women voters who represent one of the largest and most significant voter segments in the Democratic primary electorate,” Lester said. “Obama is also the most popular living president and is kind of a metaphor for being the direct opposite of Trump. So attacking Biden and Obama was very risky and it appears to have backfired. Voter movement in polls takes a while because not everyone watches the debates. So only after the debates are reported, interpreted, discussed and dissected over time and more people become exposed to the debate dynamics does it begin to show up in polls.”

Lester added, “What we are seeing here is at least partially, the residual effect of the two debates and the debate dynamics have not worked well for Kamala Harris.”

More than 200 people have declared themselves Democratic candidates in the White House race, and just over 20 are considered viable candidates. White House hopefuls and their supporters are closely following political polls more than usual because the Democratic National Committee has tightened its polling and fundraising requirements for candidates to take part in the debates in September.

Gap Between Joe Biden and Other 2020 Democrats Narrows, Poll Shows

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