Joe Biden called President Trump an “absolute fool” for not wearing a face mask during a CNN interview on Tuesday.

Biden made an appearance at a Memorial Day event on Monday wearing black face mask, while Trump has refused to wear a mask in several public events during the coronavirus pandemic. Most health experts around the world have recommended for people to wear protective face masks to help prevent the spread of COVID-19.

In the CNN interview, Biden spoke out after Trump made fun of him for wearing a mask on Twitter.

“He’s a fool. An absolute fool to talk that way. I mean, every leading doc in the world is saying you should wear a mask when you’re in a crowd. Especially when you know you’re going to be in a position where you’re going to inadvertently get closer than 12 feet to somebody,” Biden said. “It’s costing people’s lives.”

When asked if wearing a mask in public is a sign of strength or weakness, the presumptive Democratic nominee said it shows “leadership.”

“Presidents are supposed to lead, not engage in folly and be falsely masculine. It reminds me of the guys that I grew up with playing ball. They’d walk around with a ball in their hand, but didn’t like to hit very much,” Biden said.

Trump had also been taking the untested malarial drug hydroxychloroquine to prevent coronavirus, despite many health experts urging against it. He announced that he stopped taking it over the weekend.