Vice President Kamala Harris tried to buck up the Democratic Party’s biggest donors on Friday, telling about 300 of them that there was little to worry about in President Biden’s campaign.

Ms. Harris spoke to the group at a time of extraordinary turmoil among Democrats, with many hoping that she will replace Mr. Biden as the party’s nominee. But several listeners said they found the meeting overall to be of little value and even, at times, condescending, believing that the message ignored donors’ legitimate concerns about the Biden-led ticket.

Ms. Harris, of course, is in a delicate position: She must demonstrate loyalty to her boss but also be prepared to jump immediately to the top of the Democratic ticket if Mr. Biden were to withdraw.

“I will start by sharing something with all of you,” Ms. Harris told the donors, according to a listener on the call who described her remarks on the condition of anonymity, “something I believe in my heart of hearts. It is something I feel strongly you should all hear and should take with you when you leave. And tell your friends, too. We are going to win this election.”

Seven other people described the contents of the call, which was organized primarily by Impactual, an influential Democratic advisory firm for major donors. It was endorsed in part by Reid Hoffman, one of the Democratic Party’s biggest givers and a founder of LinkedIn who on Friday morning encouraged his Silicon Valley network to join the meeting. A campaign official who insisted on anonymity because of the sensitivity of the matter said Ms. Harris had joined the call at the request of the White House.

Ms. Harris, speaking by video for just over five minutes, reiterated some well-worn attack lines on former President Donald J. Trump. She pointed to his hollow call for unity at the Republican National Convention this week and the threat of Project 2025, the far-reaching policy proposals pushed by his allies. She spoke only briefly about Mr. Biden, listeners said, and did not take questions.