Former Vice President Joe Biden promised at a campaign event in Iowa on Tuesday that if he is elected president in 2020, the United States would cure cancer.

The presidential hopeful ― whose eldest son, Beau Biden, died from brain cancer in 2015 at the age of 46 ― was speaking at a campaign event in Ottumwa, one of several that he had scheduled in the state.

“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,” he said.

Biden has long made bold claims about the fight against cancer, and he announced his “Cancer Moonshot” campaign during former President Barack Obama’s final State of the Union address.

As campaign promises go, the ambition of this one overlooks a lot of complexities of the disease — like, for example, the fact that “cancer” is actually more than 100 diseases and therefore not likely treatable with a single cure-all. In his prepared statements for another event, Biden prodded President Donald Trump over his previous comments about the disease, noting that Trump “thinks windmills cause cancer.”