Press Secretary Kayleigh McEnany described administration guidelines for the coronavirus as donning a mask outdoors as "recommended but not required." Because Mr Biden kept his distance from others at the wreath-laying event, Ms McEnany called his decision to cover his face "not data-driven."
The Bidens wore black masks as they laid a wreath with a white ribbon at a memorial for the Second World War and Korean War veterans in Delaware. That image was a stark contrast to Donald Trump and Melania Trump, who did not cover their faces at Fort McHenry in Baltimore or Arlington National Cemetery.
"It's a bit peculiar that he doesn't wear a mask in his basement" while seated close to Ms Biden during interviews, the press secretary said.
When asked whether Mr Biden was just following the Centers for Disease Control and Prevention's (CDC) mask guidelines, Ms McEnany replied: "It's recommended but not required."
Mr Trump's top spokesperson said the president, who has declined to cover his face during trips to 3M and Ford facilities in recent weeks, said he is "open" to doing so – but only if circumstances warrant it.
The president reportedly has said behind the scenes that he think he would look foolish donning a face covering.