Biden -- once mocked by Trump -- now the only man on campaign trail
But with the president in quarantine after testing positive for Covid-19, his challenger has the campaign stage to himself a month before Election Day.
It is of course too soon to predict how Trump's diagnosis could impact the race for the White House, a tumultuous campaign already upended several times by history-making events.
But the irony of the latest twist in the showdown between the two septuagenarians was lost on no one Friday.
After all, just Tuesday night, Trump had doubled down on his ribbing of the 77-year-old Biden for taking too many virus precautions.
"He could be speaking 200 feet away from you, and he shows up with the biggest mask I've seen," the 74-year-old Republican incumbent sneered.
In the early months of the virus crisis, as Biden remained isolated in his Delaware home, Trump called him "Sleepy Joe" and said he was "hiding" in his basement -- a charge that his supporters lapped up and repeated ad infinitum.
But on Friday, Trump was the one forced to remain in his home, quarantining after his positive diagnosis. His doctor said he was "fatigued" but in "good spirits."
Biden meanwhile announced that he had tested negative and boarded a plane for Michigan, a key battleground state in America's Rust Belt that Trump claimed in 2016.
The former vice president to Barack Obama arrived in Grand Rapids for an event on the economy, but his speech -- which Biden delivered wearing a face mask -- of course touched on the headline of the day.
"This is not a matter of politics. It's a bracing reminder to all of us that we have to take this virus seriously. It's not going away automatically," he said -- perhaps a jab at Trump's repeated insistence that the virus will simply "disappear."
'Not about being a tough guy'
Biden then urged people to wear masks, wash their hands and practice social distancing, adding: "Be patriotic. It's not about being a tough guy. It's about doing your part."
Everyone who attended Tuesday's debate in Cleveland, Ohio had tested negative. But the virus can take several days before being detected in someone who has been infected.
Trump's family arrived in face masks, as did Biden's. But the president's entourage then removed their masks. His wife Melania has also tested positive for the coronavirus.
Biden wished the Trumps a "swift recovery," tweeting: "We will continue to pray for the health and safety of the president and his family."
The Democrat only ramped up his travel schedule in late August, after months of virtual events from his home studio or in-person events not far from Wilmington.
During that time, Trump criss-crossed the nation, holding rallies with hundreds of attendees. These were held mainly outside, but most of those present did not wear masks.
With only 32 days to go before Election Day, Trump's campaign team announced Friday that his events would either be virtual or postponed until further notice.
Meanwhile, Team Biden announced new events: his wife Jill will head to Minnesota on Saturday, while former rival Senator Bernie Sanders will campaign in New Hampshire.
And Biden's running mate, Senator Kamala Harris, was to appear in Nevada on Friday. The 50-year-old, who did not attend Tuesday's debate, has so far tested negative.
"This virus is still very much active across our country, please continue to wear a mask and maintain social distancing," she tweeted.
She is set to debate Vice President Mike Pence on October 7.
The next presidential debate between Trump and Biden is scheduled for October 15, but it was not clear if that would take place.