Larry Cohen, the chairman of the Sanders-aligned group Our Revolution, described Ms. Harris as “extremely competent.”

“She’s not Warren or Bass in terms of her background, but I don’t think it makes sense for us to criticize the reality,” he said…

“I don’t know that the left is more excited by the Harris-Biden ticket than they would’ve been otherwise,” Mr. Weber said. “But it’s clear that she’s to the left of Biden and she’s been more accountable to movements throughout her career.”

Sara Nelson, the president of the Association of Flight Attendants union and a Sanders ally, said she was focusing on how Ms. Harris, as California attorney general, had helped secure a nationwide settlement with big banks.