WILMINGTON, Del. (NewsNation) — Joe Biden is calling for a nationwide protective mask mandate, citing health experts’ predictions that it could save 40,000 lives from coronavirus over the next three months.

“Wearing the mask is less about you contracting the virus,” Biden said at a news conference in Wilmington, Delaware Thursday, alongside his newly announced running mate Sen. Kamala Harris. “It’s about preventing other people from getting sick.”

The Democratic presidential candidate said that early delays in calling for masks led to unnecessary deaths. He also responded to those who push back against such mandates.

“This is America. Be a patriot. Protect your fellow citizens. Step up, do the right thing,” Biden said.

“Every single American should be wearing a mask when they’re outside for the next three months at a minimum — every governor should mandate mandatory mask wearing,” Biden declared.

Public health officials agree that wearing masks in public slows the spread of the respiratory disease that has infected more than 5.2 million Americans.

President Donald Trump on Wednesday said at a press briefing that his administration was sending 125 million reusable masks to school districts across the nation. He urged Americans to wear masks but has opposed the idea of a national requirement and declined to wear one for months. He has worn one on occasion more recently.

When the U.S. reported 1,499 new coronavirus deaths Wednesday, the highest number of COVID-19 deaths in a single day since May, Trump pushed for schools and businesses to continue opening, and called for college football to go on despite several leading leagues’ leaders deciding to cancel this year’s season.

Biden and Sen. Harris spoke briefly Thursday in the same Wilmington hotel ballroom where they held a virtual fundraiser after appearing together as running mates for the first time Wednesday. They were briefed by public health and economic experts on the coronavirus pandemic, which has caused the deaths of more than 166,000 Americans and plunged the global economy into the worst economic recession since World War II.