Robert F Kennedy Jr is running for US president as a Democrat, but the unusual backing he is receiving from right-wingers and his history of amplifying conspiracy theories has raised suspicions about his motivations.

Over the weekend, Mr Kennedy doubled down on remarks suggesting Covid-19 may have been “ethnically targeted” to “attack” Caucasians and black people but spare Ashkenazi Jews and Chinese people.

Arguing he had “never implied that the ethnic effect was deliberately engineered”, the candidate alleged he was being smeared and cited a study published by the National Institutes of Health looking at how human genetic factors contribute to Covid transmission.

But an author of the study told the BBC’s US partner, CBS News, that its findings had “never supported” Mr Kennedy’s claims.

“This type of misinterpretation will hurt academic research to help us end the pandemic,” the author said in an emailed statement.

It is the latest debunked claim from a lawyer once celebrated as a champion of the environment, who has dedicated his energy in the past two decades to anti-vaccine activism and who last year referred to pandemic health measures as “fascism” not seen “even in Hitler’s Germany”.

Yet Mr Kennedy, 69, has seen support as high as 21% in national opinion polls since his April launch and is polling even now in the mid-to-high teens despite holding few campaign events.

That suggests some degree of disaffection among Democratic voters with President Joe Biden, who is seeking re-election at 80 years old and with an approval rating of 41%.

It may also have something to do with the challenger’s famous last name. He is the nephew of former President John F Kennedy and the third child of former Attorney General Robert F Kennedy.

Democratic strategist Kevin Walling told the BBC that Mr Kennedy’s poll numbers are “a combination of nostalgia for the Kennedy family and brand, as well as a lack of awareness about [his] views”.

He argued the support is peeling away “as more and more Democrats learn about his views on a whole host of issues”.

The Biden camp has largely ignored their long-shot rival, but White House press secretary Karine Jean-Pierre on Monday said Mr Kennedy’s comments on ethnic targeting were “vile and they put our fellow Americans in danger”.

Other members of the Democratic Party also distanced themselves from the remarks, describing them as antisemitic and anti-Asian.

Members of the Kennedy family have for years rebuked Mr Kennedy’s public statements.

“I strongly condemn my brother’s deplorable and untruthful remarks last week about Covid being engineered for ethnic targeting,” his sister Kerry wrote on Monday.

Further compounding misgivings about the rebel Kennedy is that he is unusually close with the Trump wing of the Republican Party.

In recent years, he has appeared at events pushing false claims about the 2020 election and downplaying the January 2021 attack on the US Capitol.

CBS reported in April that former Trump advisor Steve Bannon had encouraged Mr Kennedy to run “for months, believing he could be both a useful chaos agent in the 2024 race and a big name who could help stoke anti-vaccine sentiment around the country”.

Donald Trump himself praised Mr Kennedy last month, as “a very smart guy and a good guy”, while Roger Stone, a prominent Trump ally, has repeatedly promoted the idea that they run on the same ticket.

The Kennedy campaign has also received extensive friendly coverage on Fox News and other right-wing media outlets.

According to documents filed with the Federal Election Commission (FEC) on Saturday, donors who typically give to Republicans count among its top contributors so far.

“Only 20% of his donors identify as Democratic donors, while nearly 40% have a track record of giving more to [Republican] candidates and causes,” said Mr Walling, citing analysis of the FEC filing by the left-leaning Popular Information newsletter.

“It’s clear Republicans are supporting Kennedy in order to try and hurt President Biden in advance of the general election.”

Mr Kennedy’s fundraising numbers over the past three months – $6.3m (£4.8m) – outpace several of the president’s would-be Republican challengers, but is dwarfed by Mr Biden’s $72m haul over the same period.

“At the end of the day, he’s not going to deny Biden the [Democratic] nomination nor is he going to be a significant threat,” said Mark Longabaugh, another Democratic strategist.

“It’s just a gadfly candidacy making a lot of noise and I guess he settled on a strategy of figuring out the most outrageous things he can say to continue to get attention.”

He said the most chaos Mr Kennedy’s candidacy may cause will likely be in New Hampshire.

The northeastern state has long played host to the first primary contest of the presidential election season – until Democrats rearranged the calendar earlier this year at Mr Biden’s direction.

But New Hampshire Democrats have threatened to hold their first-in-the-nation primary anyway, even if Mr Biden sits it out, which could provide an opening for Mr Kennedy to get on the board.

Some older voters in the New England region once dominated by the Kennedys may still be enamoured with the dynasty, Mr Longabaugh said, but voters will ultimately be turned off by Mr Kennedy’s views and the support he receives from Republicans.

“It’s unfortunate,” he said. “There was a time, 20 to 25 years ago, when Kennedy was a very admirable person.”