Donald Trump Jr. slammed 2020 Democratic presidential candidate Joe Biden on Tuesday for announcing last week that he wants his presidential administration to cure cancer.

Addressing the crowd at Donald Trump’s 2020 campaign kickoff rally in Orlando, Fla., the president’s eldest son called out Biden for his decades in Washington as a lawmaker and as vice president, questioning why he had not pushed to find a cure before.

“What was the good one last week? Remember? Joe Biden comes out, ‘Well, if you elect me president, I’m going to cure cancer,'” Trump Jr. said. “Wow, why the hell didn’t you do that over the last 50 years, Joe?”

Curing the disease has been a priority for Biden since his son, Beau, died in 2015 following a battle with brain cancer.

“I’ve worked so hard in my career that I promise you, if I’m elected president, you’re going to see the single most important thing that changes America: We’re going to cure cancer,” Biden said last week while on the campaign trail in Iowa.

Biden oversaw the “Cancer Moonshot” when he served in the Obama administration. Its stated goal was “to make a decade’s worth of advances in cancer prevention, diagnosis, and treatment, in five years.”

Biden also oversaw the Biden Cancer Initiative, but he stepped down after announcing his presidential campaign.

The former vice president has been leading polls of the crowded Democratic presidential field as he seeks to win his party’s nomination to take on Trump in 2020.

WATCH:

Donald Trump Jr.: "Joe Biden comes out. 'Well, if you elect me president, I'm going to cure cancer.' Wow. Why the hell didn't you do that over the last 50 years, Joe?" #TrumpRallyOrlando https://t.co/FVgzrF3y67 pic.twitter.com/wa7TI9wo8H

— The Hill (@thehill) June 19, 2019

Twitter was not pleased:

Oddly, Don Jr warmed up the crowd by mocking Biden for his promise to cure cancer. 🤷‍♀️

p.s. Junior is an asshole https://t.co/9h9qQfGQJt

— Kristin (@kristinnw) June 19, 2019

@DonaldJTrumpJr wow your remarks mocking Biden for wanting more resources towards curing cancer .You have managed to show Americans how low and deplorable you can get .I lost my father to cancer like so many of families who have lost loved ones to cancer .Your remarks DEPLORABLE

— Judy Ikebata (@IkebataJudy) June 19, 2019

So sad. Trying so hard under daddy's watchful eye, talking unnecessary shit about cancer of all things, knowing damn well daddy will never love you. But yet you try try anyway.

— Bernie de Gálvez (@BernieDeGalvez) June 19, 2019

@DonaldJTrumpJr Hey Don did you know that Joe Biden lost his son to cancer no wonder he wants to find a cure how many ppl who were standing behind you or watching on TV has a kid with cancer or a family member way to go buddy

— Penny (@ScaryDairy15) June 19, 2019

@DonaldJTrumpJr Attacking & mocking @JoeBiden who lost a son to #cancer and who among us has not been affected by cancer, for stating a cure thru #CancerResearch as a campaign promise is as low as it gets. And people cheered! #Deplorable #Trump2020 #TrumpRallyOrlando

— Richard M Crasnick (@RMCrasnick) June 19, 2019