Actor Robert De Niro talks to reporters and film professionals at the 22nd Sarajevo Film Festival in Sarajevo, Bosnia, last August. (Dado Ruvic/Reuters)

Cause: Vaccine safety. Specifically the debunked link between mercury found in early childhood vaccines and autism, a claim the Centers for Disease Control and Prevention has unequivocally refuted.

Celeb: Legendary actor Robert De Niro, who’s got a Presidential Medal of Freedom and a Kennedy Center Honor medallion to add to his stack of Hollywood trophies.

What’s he doing on the panel? The 73-year-old Oscar winner was maligned last March when he initially defended the inclusion of “Vaxxed,” a documentary about the alleged danger of vaccines, at the venerable Tribeca Film Festival. After an outcry from the scientific and cinematic communities, De Niro, a founder of the festival who also has a son on the autism spectrum, pulled the film.

[7 things about vaccines and autism that the movie ‘Vaxxed’ won’t tell you]

Scene: It was a fiery panel at the National Press Club on Wednesday morning. Led by Robert Kennedy Jr., chairman of the World Mercury Project, the stage was stuffed with men who believed journalists had dropped the ball.

Kennedy spoke for 20 minutes, pointing to a leaning tower of 240 studies, three charts and several binders threatening to burst that all, according to him, proved that certain vaccines were unsafe to a certain population of children. So certain was he in the science that Kennedy announced a $100,000 reward for any journalist (or anybody) who could produce “a single study that says it’s safe to inject mothers with the levels of mercury we are currently injecting them with.”

But here’s the kicker, “You’re not gonna be able to do it. The study doesn’t exist,” said Kennedy. Also don’t call him an “anti-vaxxer.”