Donald Trump's campaign and some of his allies have initiated a pre-emptive political attack on Vice-President Kamala Harris, moving swiftly to discredit her amid speculation among some Democrats that she might replace President Joe Biden as the party's 2024 presidential candidate. Over the past 48 hours, on social media and through a series of statements, Trump's campaign and Republican allies seem to be preparing for a full-scale assault on Harris if Biden, aged 81, decides not to pursue re-election after his weak debate performance last week. Despite Biden's insistence that he is not withdrawing from the race four months before the November 5 election, and Harris's strong support for him, the Trump campaign sees little risk in attacking the vice-president now, potentially weakening her if she becomes the nominee.

Republicans have frequently criticized Harris, 59, during Biden's presidency, but the recent attacks represent a sharp and coordinated escalation, possibly linked to increased discussions about her potential to replace Biden as the Democratic presidential candidate. The National Republican Congressional Committee, overseeing House Republican races, labeled her Biden's "enabler in chief". MAGA Inc., a fundraising super PAC supporting Trump, released a statement calling her the "invasion czar". In March 2021, Biden appointed Harris to lead efforts with Mexico and Central American nations to address illegal immigration. Republicans have since used this to accuse her of failing to curb the influx of millions of illegal migrants into the United States, although she was never directly responsible for securing the southern border.

"Kamala Harris is incompetent. She's proven to be the weakest, worst vice-president in history, and she has 100 per cent supported Joe Biden in every single disastrous policy he has implemented over the last four years," said Karoline Leavitt, a spokesperson for the Trump campaign. The Biden campaign responded to the escalating Republican criticism without addressing whether the vice-president is poised to take over.

"Vice-President Harris is proud to be President Biden's running mate," said Rhyan Lake, a campaign spokesperson for Harris. "No matter what false attacks Trump and his extreme allies make, she will continue to defend the Biden-Harris record and prosecute the case against Donald Trump." The attacks on Harris by Trump's camp echo a similar strategy used against Ron DeSantis, his main Republican rival, before the Florida governor entered the 2024 election primary race last year.

Corey Lewandowski, a longtime Trump adviser, told Reuters that Harris is politically vulnerable given her role in addressing illegal immigration, among other issues that are part of extensive research the party has conducted on her record. A former senior staffer in the Trump White House, still in contact with the campaign, noted that the renewed focus on Harris makes sense.

"If Joe Biden stays on top of the ticket, given what we've seen, she takes on even more importance. But if he does step aside, she's the potential candidate. This is about defining her," the staffer said, referring to her low approval ratings in public opinion polls. Despite her consistently low approval ratings, a recent Reuters/Ipsos poll showed Harris to be as formidable an opponent to Trump as Biden. In a hypothetical matchup, Trump led Harris by a single percentage point, 43 per cent to 42 per cent.

The noise from Trump's allies contrasts sharply with the unusual silence from the typically vocal former president. Since Biden's poor debate performance, Trump has been低调, making few public appearances or statements. "This shows a maturation of the candidate himself. You can teach an old dog new tricks. He's showing increased discipline and message control," said a senior adviser to the Trump campaign familiar with internal discussions.

Even before the June 27 debate, the Trump campaign began shifting its focus to Harris, releasing an attack ad online that mocked her for repeating lines in her speeches. An online meme promoted by Republicans showed Harris repeating the same phrase "unburdened by what has been" repeatedly in remarks. Harris's defenders argue that she has become a bigger target due to her leading role in attacking Trump over abortion rights and her vigorous defense of Biden on the campaign trail.

If Biden were to withdraw from the race before the Democratic National Convention in August, there is no guarantee Harris would be the nominee. However, as vice-president, she would likely be first in line. She would benefit from Biden's substantial campaign funds and could see a large segment of Democrats rally around her to avoid a divisive intra-party fight. As the first Black vice-president in US history, she bridges the party's most reliable voting bloc. Her background and relative youth would provide a stark contrast to Trump, 78.