Robert F. Kennedy Jr faced a make-or-break Senate hearing Wednesday where he was grilled on his history of promoting vaccine misinformation and plans to upend US science agencies as he bids to become President Donald Trump's health secretary.

If confirmed, the 71-year-old Kennedy family scion and former environmental lawyer would take the helm of a department overseeing more than 80,000 employees and a $1.7 trillion budget, just as scientists warn of the growing risk of bird flu triggering a human pandemic.

Critics argue he is dangerously unqualified, citing his promotion of debunked claims linking childhood vaccines to autism, his suggestion that HIV does not cause AIDS, and accusations that he fueled anti-measles vaccine sentiment in Samoa during a 2019 visit, months before a deadly outbreak.

They also say his lucrative consulting fees for law firms suing pharmaceutical companies revealed in disclosure forms pose a conflict of interest. 

"Mr. Kennedy has embraced conspiracy theories, quacks, charlatans, especially when it comes to the safety and efficacy of vaccines, he has made it his life's work to sow doubt and discourage parents from getting their kids life saving vaccines," Democratic Senator Ron Wyden said in his opening remarks.

Kennedy hit back, saying: "News reports have claimed that I am anti-vaccine and anti-industry -- I am neither. I am pro-safety."

At the same time, the former Democrat has garnered praise for his "Make America Healthy Again" (MAHA) agenda, which riffs on Trump's "Make America Great Again" slogan and emphasizes combating the nation's chronic disease epidemic through healthier eating and promoting sustainable farming.

Complicating his path to confirmation, a conservative group founded by former vice president Mike Pence has raised concerns about Kennedy's past donations to organizations supporting abortion access -- an issue that could alienate some Republicans and hurt his chances of securing a majority of Senate votes.

Vaccine opposition

Though he has tried to soften his vaccine skepticism in recent months, Kennedy, or "RFK Jr" as he is widely known, spent two decades promoting vaccine conspiracy theories, especially around Covid-19 shots -- which he called the "deadliest ever made."

He has also stated that he exclusively drinks raw milk, claiming it "advances human health" -- a stance he maintains even as bird flu spreads among US cattle and has been shown to contaminate unpasteurized milk.

Another frequent target of his ire is the presence of fluoride in the nation's public water supplies, introduced in the mid-20th century to reduce dental cavities.

While his criticism of this practice has generated controversy, he also has the support of some in the scientific community who question whether the benefits of water fluoridation outweigh potential neurotoxic risks, particularly as fluoride is now readily available through toothpaste.