WASHINGTON (AP) — The fate of the final debates between President Donald Trump and Democrat Joe Biden was thrown into uncertainty Thursday as the campaigns offered dueling proposals for moving forward with a process that has been upended by the president's coronavirus infection.

By Thursday afternoon, it was unclear when or how the next debates would proceed, or whether voters would even get to see the two men running for the White House on the same stage again before Election Day.

The whipsaw day began with an announcement from the nonpartisan Commission on Presidential Debates, which said the next debate on Oct. 15 would be held virtually. The commission cited health concerns following Trump's infection as the reason for changing the structure of the town hall-style debate.

Trump, who is eager to return to the campaign trail despite uncertainty about his health, said he wouldn't participate if the debate wasn't in person. Biden suggested the event be delayed a week until Oct. 22, which is when the third and final debate is already scheduled.

Trump then countered again, agreeing to a debate on Oct. 22 — but only if face to face — and asking that a third contest be added on Oct. 29, just before the election. But Biden rejected holding a debate that late in the campaign.

The commission, which has the unenviable task of finding common ground between the competing campaigns, did not weigh in on any of the new proposals. The organization has come under scrutiny already during this election after the first debate between Trump and Biden deteriorated, with the president frequently interrupting his opponent and the moderator unable to take control.

For Trump, who is recovering from COVID-19 at the White House after spending three days in the hospital, the changes are an unwelcome disruption to his effort to shift focus away from a virus that has killed more than 210,000 Americans this year.

In an interview with Fox Business anchor Maria Bartiromo shortly after the commission's announcement, Trump insisted he was in "great shape" and called the idea of a virtual debate a "joke."

"I'm not going to do a virtual debate," he declared.

The president's campaign manager, Bill Stepien, said Trump would stage a rally rather than debate next Thursday, though it's not yet clear if he will be well enough to do that.

With less than four weeks until Election Day and with millions of voters casting early ballots, pressure is building on Trump to turn around a campaign that is trailing Biden nationally and in most battlegrounds, where the margin is narrower. A debate before an audience of tens of millions of television viewers could provide that reset.

But another debate could also expose Trump to political risks. GOP strategists say the party's support began eroding after his seething performance against Biden last week when he didn't clearly denounce a white supremacist group.

Trump's apparent unwillingness to change his style to win back voters he needs — particularly women — was on display again Thursday during his Fox Business interview when he referred to Democratic vice presidential nominee Kamala Harris as a "monster."

This would not be the first time Trump has skipped a debate. During the 2016 Republican primary, he boycotted the last debate before Iowa's first-in-the nation's caucuses, holding a fundraiser for veterans instead — a move he later speculated may have contributed to his loss in the state.

Boarding a flight to campaign in Arizona on Thursday, Biden said it would be "irresponsible" for him to comment on Trump's debate decision.

"We don't know what the president's going to do," Biden said. "He changes his mind every second."

It was unclear whether Biden would attend the debate by himself or whether the event would be fully scrapped. His deputy campaign manager, Kate Bedingfield, simply said Biden "looks forward to speaking directly to the American people."

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.

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 the debate, including another test that was administered on Thursday.

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Associated Press writers Bill Barrow in Wilmington, Delaware, and Jill Colvin in Washington contributed to this report.