President Trump’s hospitalization has plunged an already volatile race into extraordinary uncertainty, sidelining the president indefinitely with a month until Election Day and making the pandemic a more urgent and delicate issue for Joseph R. Biden Jr.
On Saturday, Mr. Trump remained at Walter Reed National Military Medical Center, where he sought to send a reassuring message that he was “starting to feel good.”
“I think I’ll be back soon,” Mr. Trump, seated at a dark-wood table and wearing a jacket but no tie, said in a video posted on Twitter. “And I look forward to finishing up the campaign the way it was started and the way we’ve been doing.”
But given the uncertain course of the virus, it could be weeks before Mr. Trump can return to the campaign. His aides canceled rallies that were to be held in Florida on Friday and Wisconsin on Saturday and said they would consider future events on a “case-by-case basis.”
Mr. Trump acknowledged that the next few days could be “the real test” in determining his medical condition.
Mr. Biden has for months sought to make the race a referendum on Mr. Trump’s stewardship of the pandemic, but that task has become more sensitive in light of Mr. Trump’s hospitalization.
“I’m in a little bit of a spot here because I don’t want to be attacking the president and the first lady now,” Mr. Biden said at a virtual event on Saturday with members of the Amalgamated Transit Union, adding that he had prayed for the couple’s quick recovery.
Still, Mr. Biden criticized the Trump administration for not requiring transit riders to wear masks and for not doing more to get personal protective equipment for workers. “I promise you, I’m going to get you all the P.P.E. that’s necessary,” Mr. Biden said.