Washington DC - Vice President Kamala Harris is engaged in a delicate balancing act, playing cheerleader for President Joe Biden while standing by as a leading contender to replace him if he ends his re-election bid.

Biden's dismal performance in last week's debate with Donald Trump has triggered panic in much of the Democratic Party as people question whether Biden is physically and mentally able to beat Trump and serve another four years.

Former congressman Tim Ryan, while professing his admiration for Biden, wrote in a piece for Newsweek that "the Democratic nominee in 2024 should be Kamala Harris."

Harris herself has not said anything in public, except to express loyalty to her boss.

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"Look, Joe Biden is our nominee," she said in an interview with CBS News. "We beat Trump once, and we're going to beat him again, period."

She said she was proud to be on the current ticket with the president.

Minutes after the debate, Harris had rushed onto TV to defend Biden, saying he had started off slowly in the clash with Trump but finished strong.

The official schedule for Biden on Wednesday says he had lunch with Harris, which is not a regular event, though it was a weekly fixture for Biden when he was vice president under Barack Obama.

Harris (59) is the first woman, the first Black person, and the first person of Asian origin – her mother was from India – to hold the job that puts her a heartbeat from the presidency.

Harris would become president if Biden died in office or became incapacitated, but she would not necessarily replace Biden if he were to end his candidacy, and Biden has insisted he has no plans to do so.

"For three and half years, there has always been this drumbeat that someone other than the VP should be the Democratic candidate," said Ange-Marie Hancock, professor of political science at The Ohio State University.

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Hancock said it was possible an "undercurrent of racism and sexism" was at work against Harris.

For years, Harris has been less popular among Americans than other Democrats seen as possible candidates, such as California Governor Gavin Newsom or his Michigan counterpart Gretchen Whitmer.

US media have reported extensively on mistakes she made early in this administration, mainly on the diplomatic front and on tension among her staffers.

But Hancock said things could turn in Harris's favor because she has spent time out visiting battleground states, in particular, to promote abortion rights as it came under repeated fire from conservative judges and governors.

Harris is sometimes criticized as disappointing as an orator. But she got a warm welcome recently when she made a tour of universities that was focused on schools with high numbers of minority students.

A CNN poll released Tuesday had Harris doing better than Biden against Trump, although not beating him.

This poll gave Harris 45% of voter intentions against 47% for Trump, while Biden scored 43% to 49% for the Republican former president in a race between the two men.

In the event Biden was to drop out, Harris, thanks to her name recognition, her ties to powerful people in the government, and the prospect for brisk fundraising, would go into the Democratic convention next month in a position of strength.

But the Republicans are ready and waiting.

"Kamala Harris is very much on the GOP's radar," Hancock said.

The Trump campaign on Wednesday broadcast a video montage of Biden suffering falls and other embarrassing moments and questioned whether he can serve another term.

It concludes with the question, "And you know who is waiting behind him, right?" and footage of Harris laughing.