WASHINGTON (AP) — President Donald Trump vowed Thursday to skip next week's debate with Democratic nominee Joe Biden after organizers said it would be held virtually because of the president's COVID-19 diagnosis — more evidence that the race will be defined by the coronavirus despite the White House's attempts to make it about almost anything else.

"I'm not going to do a virtual debate," Trump told FOX Business anchor Maria Bartiromo, moments after the nonpartisan Commission on Presidential Debates announced the changes.

Biden's campaign insisted its candidate was ready to move forward with the second presidential debate next Thursday in Miami, but the future of the event is now in serious doubt.

The commission made the decision unilaterally, citing the need "to protect the health and safety of all involved with the second presidential debate." A person familiar with the matter said some associated with the production of debate No. 2 raised safety concerns after Trump tested positive for the virus following the first debate last week in Cleveland.

When Republican Mike Pence and Democrat Kamala Harris met for their only vice presidential debate in Salt Lake City on Wednesday night, they shared a stage but were separated by plexiglass to prevent the spread of the virus, despite both having previously tested negative.

Trump is thought to be trailing in key battleground states. Even before his COVID-19 diagnosis, the president was widely criticized for his chaotic performance during the Cleveland debate. Next week's faceoff in Miami, and a third one set for the following week in Nashville, would have given him a chance to reset the election and potentially change its trajectory in front of a national television audience — but he now appears ready to give up that up.

Trump has vowed to return to the campaign trail as soon as he's able. Still, the commission's move shows how much the pandemic has upended the presidential race, even as the Trump administration has insisted for months that the country has turned the corner. The president has even said he considers his getting the virus a plus, though it has claimed the lives of more than 200,000 Americans.

"I don't want to do a virtual debate because (a) virtual debate is a joke. There's no reason. I'm in great shape," Trump said.

He then reverted to one of his mainstay attacks, that Biden spent months focusing too heavily on virtual campaigning from his home in Delaware, even though the Democrat has begun crisscrossing the country in recent weeks.

"I don't have the luxury of staying in a basement all day," Trump said.

Boarding a flight to campaign in Arizona on Thursday, Biden said it'd be "irresponsible" for him to comment. "We don't know what the president's going to do. He changes his mind every second" and could ultimately end up debating anyway," Biden said.

Still, Trump's campaign manager promised that the president will stage a rally rather than debate — though its not yet clear he will actually be well enough for that.

"For the swamp creatures at the Presidential Debate Commission to now rush to Joe Biden's defense by unilaterally canceling an in-person debate is pathetic," Bill Stepien, Trump campaign manager, said in a statement. "The safety of all involved can easily be achieved without canceling a chance for voters to see both candidates go head to head. We'll pass on this sad excuse to bail out Joe Biden and do a rally instead."

Biden aides argued that Trump's pulling out could be a boon to their candidate. Given reactions to the first debate, they believe most voters, especially undecided voters, will see the president as avoiding a second one out of his own interests — not because he dislikes the format.

"Vice President Biden looks forward to speaking directly to the American people," deputy Biden campaign manager Kate Bedingfield said in a statement.

Biden spokesman Andrew Bates went further, tweeting, "Unsurprisingly, one candidate is leading while the other is whining."

"Americans are sacrificing and suffering because of Donald Trump's failed response, but yet again in his weakness he's proving that he only cares about himself - not even his supporters," Bates added.

A Biden aide said it would be up to the debate organizers to decide whether the former vice president would get a 90-minute broadcast to himself. Aides did not immediately say what the campaign's preference might be, and the lead Biden negotiator is traveling back from Salt Lake City, after the vice presidential debate, and was not immediately engaged with the commission Thursday morning.

Asked about participating by himself, Biden responded, "We don't know enough to know right now."

"You never know what's going to come out of his mouth," he said of Trump.

Biden said earlier in the week that he was "looking forward to being able to debate" but added that he and Trump "shouldn't have a debate" as long as the president remains COVID positive.

The commission had announced earlier Thursday that the candidates would "participate from separate remote locations" while the moderator remained in Miami. Moments later, Trump vowed not to participate at all.

Trump fell ill with the virus last Thursday, just 48 hours after debating Biden in person in Cleveland. While the two candidates remained a dozen feet apart during the debate, Trump's infection sparked health concerns for Biden and sent him to undergo multiple COVID-19 tests before returning to the campaign trail.

Trump was still contagious with the virus when he was discharged from Walter Reed National Military Medical Center on Monday, but his doctors have not provided any detailed update on his status. According to the Centers for Disease Control and Prevention, those with mild to moderate symptoms of COVID-19 can be contagious for as many as — and should isolate for at least — 10 days.

Biden has repeatedly tested negative for the virus since, but his campaign has refused to say whether his going into quarantine was ever discussed. After Arizona, the former vice president was set to campaign Friday in Las Vegas.

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Associated Press writer Bill Barrow contributed to this report from Wilmington, Del.