For years it's been a Republican scare tactic.

A vote to reelect President Joe Biden, the GOP often charges, is really a vote for Vice President Kamala Harris. It's an attack line sometimes tinged with racist and misogynist undertones and often macabre imagery.

But after Biden's dismal performance at last week's presidential debate, which has sparked Democratic calls for him to step aside, what was once dismissed as a far-right conspiracy — Harris replacing Biden — could now have a chance of coming to pass. And Republicans, including Donald Trump, are ramping up their attacks.

Trump and his allies have been rolling out new attack lines against Harris, insulting her abilities, painting her as Biden's chief enabler and accusing her of being part of a coverup of his health. It's an effort, campaign officials insist, that is not a reflection of their concerns about a potential change at the top of the ticket, given Biden's insistence he is not leaving the race.

But in a post marking Independence Day on his Truth Social site Thursday, Trump singled out Harris, calling her his “potentially new Democrat Challenger” and giving her a new derisive nickname: “Laffin' Kamala Harris.”

“She did poorly in the Democrat Nominating process, starting out at Number Two, and ending up defeated and dropping out, even before getting to Iowa, but that doesn't mean she's not a highly talented' politician! Just ask her Mentor, the Great Willie Brown of San Francisco,” he wrote. ( Harris dated Brown in the mid-1990s.)

The post came after Trump campaign senior advisers Chris LaCivita and Susie Wiles released a statement earlier this week that offered a different, but similar, moniker, calling her Biden's "Cackling Copilot Kamala Harris.”

Trump also posted an expletive-laced video, which was first been reported by the Daily Beast, in which he was captured on the golf course calling Biden an “old broken down pile of crap” and declaring that he'd driven the president from the race. (Trump, in interviews, has repeatedly said he did not expect Biden to be pushed aside.)

“He's quitting the race,” Trump said. “And that means we have Kamala. I think she's going to be better. She's so bad. She's so pathetic," he said.

Allies have also joined the attacks, painting Harris as a chief defender of Biden's faculties and accusing her of lying to the American public.

Biden, the White House and his campaign insist he has no plans to drop out of the race. During an interview with ABC News that aired Friday night he said that only “the Lord Almighty” would drive him from the race.

White House press secretary Karine Jean-Pierre pushed back against the tenor of attacks against Harris, particularly Trump's decision to invoke a decades-old relationship and other sexist rhetoric.

“I think it's gross, I think it's disturbing,” Jean-Pierre told reporters Friday aboard Air Force One. “She should be respected in the role that she has as vice president. She should be respected like any other vice president before her who was in that room. It is appalling that, I'm going to be careful here, that a former president is saying that about a current vice president. And we should call that out — it is not OK.”

It remains unclear how Harris would fare against Trump, compared to Biden. Replacing a candidate this late in a presidential cycle — much less an incumbent president who has already sailed through the Democratic Party's primaries — would be unprecedented in modern history, and the mechanics are complicated and potentially messy.

Polling shows that Harris' favourability ratings are similar to Biden's and Trump's. A June AP-NORC poll found about 4 in 10 Americans have a favourable opinion of her. But the share of those who have an unfavourable opinion is slightly lower than for Trump and Biden, and about 1 in 10 have no opinion of her yet.

Harris, at 59 years old, would be a marked generational contrast to Trump, who is 78 years old and has also shown signs of aging. As the first woman, the first Black person and the first person of South Asian descent to serve as vice president, she would also chart a potentially barrier-breaking candidacy that could draw the support of women, minority voters and younger people — groups with whom Trump has been working to make significant inroads.

Harris has also been the Biden administration's leading voice on abortion rights, an animating issue for Democrats since the overturning of Roe v. Wade that could again motivate turnout this fall.

Trump's campaign, however, said it was confident in Trump's chances regardless of his opponent and dismissed the idea that Harris might pose a greater challenge to Trump, seeing her as a more polarizing figure than the president.

“President Trump will beat any Democrat on November 5th because he has a proven record and a agenda to Make America Great Again,” LaCivita and Wiles said in their statement.

One campaign official suggested the focus on Harris was more of a reflection of the current media focus on the Democratic ticket than a belief that she will ultimately replace Biden.

While the party has plenty of opposition research on Harris at the ready thanks to her 2020 campaign and her years as vice president, at the end of the day, they argue, the Biden record is the Harris record, and if she were to replace Biden, Trump aides wouldn't face a totally different race.

Harris, for instance, was tapped by Biden to lead the administration's response to drivers of the border crisis, tying her to one of his weakest issues. And if he does drop out, they argue, voters will have issues trusting the administration, Harris and the press for not shedding light on Biden's weaknesses sooner.

“The economy's still the economy, the border's still the border, there's still global conflicts," said Trump campaign spokesperson Danielle Alvarez. “And changing the person at the top of the ticket doesn't change those realities for American voters.”