By wearing a mask at a Memorial Day ceremony in DE - and by changing his Twitter profile to a photograph of him donning the black covering - Biden signalled he is putting the coronavirus front and centre during the USA presidential race in a nation increasingly divided over the pandemic.
Trump has openly refused to wear a face mask.
The stand-off played out as the United States surpassed a jarring milestone yesterday in the coronavirus pandemic: 100,000 deaths. However, Mr Trump, despite at times saying he would be willing to wear a mask, has continued not to do so at press conferences and recent out-of-state visits.
Asked whether wearing a mask projected weakness or strength, Mr Biden chose a different description.
Following his Tuesday remarks, Biden changed his profile picture on Twitter to the one of him wearing a black mask during a Memorial Day ceremony.
He added: "Presidents are supposed to lead, not engage in folly and be falsely masculine".
Mr Trump has refused to appear in public wearing a mask, and numerous Americans who are bare-faced at demonstrations calling for states to immediately reopen are supporters of the president.
In his video address Wednesday evening, Biden argued that the death toll milestone "could have been avoided", as he referenced a Columbia University study that indicated earlier action on social distancing could have saved 36,000 lives. Cornyn shared a photo of himself in a mask and encouraged others to also wear one.
Twitter has put a fact-check alert on Trump's tweets regarding mail-in ballots. "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.
Mr Trump responded: "Joe Biden can wear a mask, but he was standing outside with his wife, flawless conditions, ideal weather".
Trump is gambling that his call to swiftly end lockdowns will win over undecided voters.