GEOFF BENNETT: With the intense focus on the Republican primary this election season, one Democratic underdog has been getting attention for his controversial comments, spreading misinformation on a range of topics.

That was on display again today, as Robert F. Kennedy Jr. testified on Capitol Hill at a hearing convened by House Republicans.

Lisa Desjardins explores what has captured the attention of some voters.

LISA DESJARDINS: The first major 2024 surprise, Democrat Robert F. Kennedy Jr. has sparked double-digit support in polls, controversy on airwaves and a headache for President Joe Biden.

This spring, the 69-year-old environmental lawyer launched his campaign highlighting his famous political family, speaking in Massachusetts with a sea of "Kennedy for President" signs.

ROBERT F. KENNEDY JR. (D), Presidential Candidate: I have come here today to announce my candidacy for the Democratic nomination for president of the United States.

(CHEERING AND APPLAUSE) LISA DESJARDINS: An echo of the past impossible to miss.

ROBERT F. KENNEDY, Former U.S. Attorney General: I am announcing today my candidacy for the presidency of the United States.

LISA DESJARDINS: The son of Senator Robert F. Kennedy, who was assassinated month after launching his campaign for president and nephew of John F. Kennedy, killed while president.

ROBERT F. KENNEDY JR.: My father and my uncle had a vision for America.

LISA DESJARDINS: On one hand, this Kennedy leans into his family's legacy with views that are anti-war, pro-environment and to talk of ending divide.

ROBERT F. KENNEDY JR.: The possibility they foresaw is still alive, the America that almost was and yet may be.

It's time to unlearn the reflexes of fear and blame and find ways to unify ourselves and turn our country around.

LISA DESJARDINS: But, on the other hand, Kennedy stokes his own controversy, conspiracy, and at times racial confrontation, as in the latest headlines.

The New York Post obtained video of Kennedy at a dinner with reporters saying the coronavirus targets specific racial groups.

ROBERT F. KENNEDY JR.: COVID-19 is targeted to attack Caucasians and Black people.

The people who are most immune are Ashkenazi Jews and Chinese.

LISA DESJARDINS: Outcry was immediate.

The head of the Anti-Defamation League wrote that: "The idea feeds into conspiracy theories, lacks any factual basis and is nuts."

The Jewish group has put out research in the past debunking racist COVID theories as dangerous.

Kennedy tweeted out that his words were misconstrued, yet doubled down on the idea of ethnic targeting.

He linked to a study.

But that study does not say any group is targeted by or immune from COVID.

Instead, it focused on some cell traits that might make things easier or harder for the virus.

That study was early in the pandemic.

It is now clear, of course, that COVID hit brutally across ethnic populations.

At Kennedy's fiery hearing on Capitol Hill today, Democrats blasted him.

REP. DEBBIE WASSERMAN SCHULTZ (D-FL): Your bizarre, unproven claim echoes that same historic slander of labeling Jews and Chinese people as a race and that Jews and, in this case, Chinese people somehow managed to avoid a deadly illness that targets other groups for death.

You do see that, yes or no?

ROBERT F. KENNEDY JR.: You're misstating... REP. DEBBIE WASSERMAN SCHULTZ: No.

No, no, no.

ROBERT F. KENNEDY JR.: Yes, you are.

REP. DEBBIE WASSERMAN SCHULTZ: I quoted it.

I quoted what you said earlier.

ROBERT F. KENNEDY JR.: You are slandering me incorrectly.

ROBERT F. KENNEDY JR.: What you're saying is dishonest.

REP. JIM JORDAN (R-OH): The time belongs to the gentlelady from Florida.

(CROSSTALK) ROBERT F. KENNEDY JR.: ... and myself.

LISA DESJARDINS: When presented with many of his past statements, Kennedy told lawmakers he is misunderstood.

ROBERT F. KENNEDY JR.: My views are constantly misrepresented.

I believe vaccines should be tested with the same rigor as other medicines and medication.

LISA DESJARDINS: But Kennedy has pushed a host of disproven ideas that undermine all vaccines, including the idea that vaccines make people sicker, when data show they overwhelmingly save lives.

ERIN O'BRIEN, University of Massachusetts Boston: The more he talks, the more he gets himself in trouble.

LISA DESJARDINS: Erin O'Brien is a political science professor at the University of Massachusetts Boston.

She's heard Kennedy pop up on podcasts spouting a series of unproven conspiracies, some debunked, questioning what causes HIV, alleging that a pesticide makes people transgender and, as on the Joe Rogan podcast, baselessly suggesting that vaccines cause autism.

ROBERT F. KENNEDY JR.: And everybody will say, oh, there's no study that shows autism and vaccines are connected.

That's just crazy.

And that's people who are not looking at science.

LISA DESJARDINS: The study Kennedy has pointed you in the past was retracted.

And several mass studies have proven the opposite, no link.

But Professor O'Brien says Kennedy has scored politically.

ERIN O'BRIEN: The vast majority of us are not scientist.

And you go to school for a long time for that.

You learn a rigorous scientific method.

So he's smart as a politician saying: I trust you.

You look at the facts.

But what he means is, Google some stuff and don't discern which facts should be believed, which are peer-reviewed.

LISA DESJARDINS: But is he a real threat to Joe Biden?

Kennedy has stayed consistently in the low teens in head-to-head polls, not nothing, but not yet within real striking distance.

ERIN O'BRIEN: I honestly think he's a vessel, he's a symbol for dissatisfaction, going back to the fact that most individuals don't want to vote for Donald Trump, nor do they want to vote for Joe Biden.

So, Robert F. Kennedy right now is the beneficiary of some of that disdain.

LISA DESJARDINS: Kennedy has ginned up interest from corners of both parties, a rare Democrat appearing regularly on conservative media.

Also rare, Donald Trump has praised him.

They share a goal after all, defeating Joe Biden.

For the "PBS NewsHour," I'm Lisa Desjardins.

GEOFF BENNETT: And to help put some of Mr. Kennedy's comments into context, we're joined by Dr. Paul Offit, who is a member of an FDA advisory committee on vaccines.

He's also director of the Vaccine Education Center at the Children's Hospital of Philadelphia.

Thank you for being with us.

DR. PAUL OFFIT, Children's Hospital of Philadelphia: Thank you.

GEOFF BENNETT: So, RFK Jr. is widely known as an anti-vaccine activist.

He has a much larger platform now as he runs for president.

He says that many if his views are misunderstood, they're taken out of context.

Help us understand what he's been promoting and what the science tells us about it.

DR. PAUL OFFIT: Well, he's been promoting false information about vaccines.

He's been promoting the notion that vaccines cause autism, which is clearly not true, or cause a variety of other chronic diseases, like diabetes or multiple sclerosis or attention-deficit disorder.

And that's all not true.

So, what he does is, by putting misinformation out there, he causes people to make bad decisions that put themselves and their family at risk.

GEOFF BENNETT: You also point to one episode where he spoke out against the measles vaccine.

What was the impact of that?

DR. PAUL OFFIT: In Samoa, there were two children that died immediately following receipt of a measles vaccine.

And the way it works into Samoa is, they have a MMR vaccine in powdered form.

It needs to be diluted in water.

Two nurses made a mistake.

Instead of diluting it in water, they diluted it in a muscle relaxant.

Those children stopped breathing and died immediately.

Now, very quickly, within two weeks, it was realized what that mistake was.

It was a nursing error.

But, nonetheless, RFK Jr. seized on that.

He flooded Facebook with information that measles vaccine is killing children in Samoa.

He went to Samoa.

He met with anti-vaccine activists.

He met with senior officials in Samoa and kept the drumbeat alive that measles vaccine was killing children in Samoa.

As a consequence, vaccination rates fell from 70 percent to 30 percent.

And between September and December of 2019, there was a massive measles epidemic.

In this island nation of 200,000 people, there were 57,000 cases of measles and 83 deaths.

Most of those deaths were in children less than four years of age.

And Robert F. Kennedy Jr. had everything to do with that.

And that shows you how disinformation can kill.

GEOFF BENNETT: He's drawn criticism most recently for saying that COVID ethnically targets -- that's the phrase he used -- white and Black people, and not certain Jewish and Chinese people.

Is there any evidence to support that?

DR. PAUL OFFIT: No, there's evidence that doesn't support it.

Actually, the paper that he points to, he should have read exactly when that paper was submitted for publication.

It was submitted before COVID ever came into the United States.

Those researchers were trying to make a prediction based on certain so-called genetic differences among racial or ethnic or religious groups as to who would likely or not likely get COVID.

Well, now we know that they were wrong.

COVID was an equal opportunity employer.

Seven million people have died.

It doesn't matter what your racial or ethnic or religious background was.

The only thing that matters is your age, number of comorbidities, whether you're immune-compromised.

So that prediction that was made by that paper was wrong.

Nonetheless, he still held on to it as fact.

GEOFF BENNETT: Robert F. Kennedy Jr. says that his views shouldn't be censored, that people should be free to do their own research.

In your view, what are the problems with bad information being on the same playing field with good information, with scientific data?

DR. PAUL OFFIT: Well, I think the Samoa outbreak told you a lot about what it means to have bad information out there.

I think the notion that people can therefore do their own research.

But the fact of the matter is, when he says, do your own research, what he really means is look on the Internet and find out other people's opinions.

I mean, most people don't look at all the original papers.

And so, for example, if you look at the paper that he cited as showing why there are racial or ethnic differences in susceptibility, you would see how flawed that paper was.

But you do need, to some extent, a scientific background.

In any case, it's hard for him -- to watch him put this kind of misinformation out there continually.

He definitely is showing what misinformation can do.

And, as a consequence, children are suffering this.

GEOFF BENNETT: More than three years after the start of the pandemic, as you see it, how has misinformation taken hold?

DR. PAUL OFFIT: The problem, I think, is social media, which is a source of great information and awful information.

And people feel that they can go on social media and know just as much as anyone that's giving them advice.

And I think -- sadly, I think public health institutions have been marginalized at some level, whether it's the FDA, or the CDC, or Dr. Fauci, or Dr. Walensky at the CDC, and others.

And so I think we have become a cynical, litigious society, not to our advantage.

We kind of leaned into a libertarian left hook that people didn't like being told that they should mask or didn't like being told that they should be vaccinated.

And, as a consequence, we pushed back on these public health measures, which only hurt us.

GEOFF BENNETT: Dr. Paul Offit, thanks so much for your insights.

We appreciate it.

DR. PAUL OFFIT: Thank you.