Donald Trump Jr. slammed 2020 Democratic presidential candidate Joe BidenJoe BidenCast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response Biden tells CNN town hall that he has benefited from white privilege MORE on Tuesday for announcing last week that he wants his presidential administration to cure cancer.

Addressing the crowd at President TrumpDonald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE’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?"

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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.