“His reckless personal conduct since his diagnosis, the destabilizing effect it’s having in our government is unconscionable,” Mr. Biden said while campaigning in Nevada.

“He didn’t take the necessary precautions to protect himself or others,” said Mr. Biden, the Democratic presidential nominee. “And the longer Donald Trump is president, the more reckless he gets. How can we trust him to protect this country?”

Mr. Trump was hospitalized from last Friday until Monday after testing positive.