Poll numbers for Sen. Kamala Harris, D-Calif., have fallen as much as 13 points from her first debate in June when she challenged former Vice President Joe Biden, with one Democratic pollster attributing the drop from the "sugar high" to an unfocused message.

Harris garnered only 7% in the Quinnipiac University poll released Tuesday, down from 20% in the July 2 poll and from 12% in the July 29 survey.

Otherwise, Harris has polled only in the single digits in the Quinnipiac survey since her campaign began in January.

One Democratic pollster explained Harris' drop to Axios this way: "I don't think anybody can figure out what her message is.

"We know what [Elizabeth] Warren's message is, and Bernie [Sanders'] message — and we kinda know Biden's message, even if he's not delivering it very well.

"But who is she really?" the pollster asked. "And what is her message?"

Harris is falling in at least one other national poll, Axios notes:

Only 20% of Democratic primary voters rated her performance in the Detroit debates as "excellent," according to a Politico/Morning Consult poll, also out Tuesday. That compared with 43% who said the same of her showing in the Miami debate in June.

Only 9% of those voters said they preferred Harris, according to the poll, down 3 percentage points from pre-debate polling results — and her net favorability rating has dropped by 11 points.

While the Harris campaign declined to comment to Axios, one other Democratic pollster was optimistic.

"None of this has to be fatal, but she's got to get out of this rut," the pollster told Axios.