Less than 24 hours after President Biden’s faltering performance at a debate in Atlanta, Vice President Kamala Harris was standing before a crowd of supporters in a crucial battleground state on Friday, defending his record and his fitness for office.
But with Democrats openly discussing replacing Mr. Biden on the ticket, Ms. Harris was also effectively making a case for herself.
She spoke clearly about Mr. Biden’s record, in ways that the president did not the night before. She tried to draw a contrast between Mr. Biden and his opponent, former President Donald J. Trump, whose lies and falsehoods were on full display at the debate.
But another striking contrast — between Ms. Harris and her boss — was on the minds of Democrats as well. Although the prospect of removing Mr. Biden from the ticket remains far-fetched, Ms. Harris would most likely be one of a half-dozen candidates vying for the presidential nomination if Mr. Biden pulled out.
“You have to ask, how did we get here?” former Senator Claire McCaskill, Democrat of Missouri, said on Thursday evening, after Ms. Harris gave a strong post-debate interview on CNN. “How do we get to the point that we’re spending a whole lot of time talking about the vice president tonight, instead of talking about the president?”
Ms. Harris, 59, has spent much of her time as vice president struggling to distinguish herself in a role that is by definition a supporting one. Her polling has remained stubbornly low, tracking with Mr. Biden’s. And as recently as last year, some Democrats were privately fretting that she was a liability for the campaign.
Still, with the Biden campaign in crisis, there is a renewed focus on Ms. Harris as she tries to calm a panicking Democratic Party. On Friday in Nevada, she made her loyalty to Mr. Biden clear.
“In a real leader, character matters more than style,” Ms. Harris said. “Donald Trump simply does not have the character to be president of the United States.”
Ms. Harris has been campaigning intensely for months, winning praise from some former critics for her work on abortion rights, Gaza and Black maternal health.
Her aides say she connects with voters who are not a natural fit for Mr. Biden, such as minorities and younger voters. In a span of 12 hours this month, she traveled to Atlanta to speak about economic opportunities for Black men, who have wavered in their support for Mr. Biden, before traveling to a summit in Switzerland to rally support for Ukraine.
She has also become one of Mr. Biden’s fiercest defenders. In February, she delivered a legal takedown of the special counsel report that concluded that Mr. Biden was a “well-meaning, elderly man with a poor memory” and had “diminished faculties in advancing age.”
On Friday, some Democrats said Ms. Harris’s performance after the debate was exactly what they had wanted to see on the debate stage in Atlanta.
She spoke about the administration’s position on abortion after Mr. Biden fumbled on an issue that should have been a slam-dunk for him. During her appearance on CNN, she sharply criticized Mr. Trump as being “all over the place” on the issue and focused on the fact that his Supreme Court picks were crucial to overturning Roe v. Wade.
“V.P. Harris channeled the feelings of millions of Americans last night in her real-talk defense of President Biden and total takedown of Donald Trump,” said Quentin James, co-founder of the Collective PAC. “We wanted to see more of that righteous indignation on the debate stage.”
Mr. James said he hoped the administration sent Ms. Harris out more: “She’s the best spokesperson we have right now.”
In her CNN interview, Ms. Harris acknowledged a “slow start” for Mr. Biden during the debate. But she also tried to drill down on what she saw as the bottom line: that a 90-minute debate was less important than three and a half years of governing.
On Friday, she echoed that same message. “In the Oval Office, negotiating bipartisan deals, I see him in the Situation Room keeping our country safe,” Ms. Harris said, adding that the race would not be decided by “one night in June.”
Fletcher N. Smith Jr., a former state representative in South Carolina who worked as a surrogate for the Biden campaign in 2007 and 2020, said there needed to be “a real conversation in the Democratic Party about where our leadership is going.”
But Mr. Smith said was nervous about Ms. Harris leading the ticket because of the way she handled migration, a top concern of voters. Ms. Harris has faced blowback over the record number of crossings at the southern border because Mr. Biden, early in his term, tasked her with addressing poverty and corruption in the region.
“If the Democrats decided to nominate her to be at the top of the ticket, we’ll still be in the same place we’re in today,” Mr. Smith said. “It’ll still be a close race.”
At Ms. Harris’s campaign event on Friday, anxiety was high.
Stephen Stubbs, an undecided voter, questioned Mr. Biden’s mental acuity.
“Who’s running the country?” Mr. Stubbs said he wondered after watching the debate. “Let Kamala in!” he added, hoping Mr. Biden would step down.
Camille Kauer, a Black woman from North Carolina who attended Mr. Biden’s rally in Raleigh on Friday, called Mr. Biden and Ms. Harris a “dynamic duo.”
She said she was excited by the prospect of Ms. Harris becoming president one day. Ms. Harris has already made history as the first woman, the first African American and the first Asian American to serve as vice president.
But Ms. Kauer had doubts about whether Ms. Harris would get a shot at the top job.
“The party’s not really good at supporting Black women,” she said.
Simon J. Levien contributed reporting from Las Vegas.