During his father’s kickoff rally on Tuesday, Donald Trump Jr. attacked former Vice President Joe Biden‘s statement that he wants his administration to cure cancer.

Speaking to the crowd at his father’s 2020 reelection event, Trump Jr. mocked the Democratic candidate for his goal, questioning why he hadn’t yet cured the disease in his 50 years as a politician. “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?” Later in that same rally, Trump himself also claimed that he would cure cancer.

Biden has made fighting cancer a priority after his son, Beau Biden, died from brain cancer in 2015. Addressing supporters at a campaign stop in Iowa last week, Biden said, “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.”

While he was Barack Obama‘s vice president, Biden oversaw the “Cancer Moonshot,” a project with the goal of making “a decade’s worth of advances in cancer prevention, diagnosis, and treatment, in five years.” He also ran the Biden Cancer Initiative but stepped down from his role in order to focus on running for president.

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Biden has been a prime target for many in the Trump Administration, as polls currently show him as the president’s most formidible opponent. Several polls have shown the former vice president leading Trump by as much as 13 points in key battleground states like Michigan and Wisconsin, angering the president. As Biden continues to gain support and rise above other Democratic challengers, Trump has singled him out as a foil and begun blasting him with insults. While Tuesday’s event only contained one Biden-focused insult by Trump, his soon took up the mantle before his father came on stage, mocking and insulting the Democratic candidate and making his father proud.