President Donald Trump on Sunday declared he was ready to return to the campaign trail despite unanswered questions about his health on the eve of a Florida rally meant to kick off the stretch run before Election Day.

His impending return comes after the White House doctor said he was no longer at risk of transmitting the coronavirus but did not say explicitly whether Trump had tested negative for it. The president insisted he was now “immune” from the virus, a claim that was impossible to prove and added to the unknowns about the president’s health.

“I’m immune,” Trump said in an interview on Fox News Channel’s “Sunday Morning Futures.” “The president is in very good shape to fight the battles.”

In a memo released Saturday night by the White House, Navy Cmdr. Dr. Sean Conley said Trump met the Centers for Disease Control and Prevention criteria for safely discontinuing isolation and that by “currently recognized standards” he was no longer considered a transmission risk. The memo did not declare Trump had tested negative for the virus.

But sensitive lab tests — like the PCR test cited in the doctor’s statements — detect virus in swab samples taken from the nose and throat. Some medical experts had been skeptical that Trump could be declared free of the risk of transmitting the virus so early in the course of his illness. Just 10 days since an initial diagnosis of infection, there was no way to know for certain that someone was no longer contagious, they said.

His return to full-fledged rallies will be in Florida on Monday, a comeback that comes with the president facing stubborn deficits in the polls. The Trump campaign and White House has not indicated that any additional safety measures will be taken to prevent the transmission of the virus among those traveling on Air Force One, at the event site or at rallies scheduled for Pennsylvania and Iowa later in the week.

Campaign officials have signaled that Trump will be traveling nearly every day the rest of the campaign, and sometimes making more than one stop, an aggressive schedule for a 74-year-old who was hospitalized just days ago.

And with the virus again dominating the national discourse, the Trump campaign has released an ad featuring Dr. Anthony Fauci praising the president’s leadership — but the nation’s leading infectious disease expert on Sunday objected to being included.

“The comments attributed to me without my permission in the GOP campaign ad were taken out of context,” Fauci said in a statement, adding that he was talking broadly about public health officials’ response to the pandemic. “In my five decades of public service, I have never publicly endorsed political candidates.”

Tim Murtaugh, Trump campaign communications director, responded by saying that “these are Dr. Fauci’s own words” and said they were praising the administration’s response.

On Sunday, Trump asserted in a tweet that he had “total and complete sign off from White House Doctors” to fully return to the campaign trail, insisting he can no longer spread the disease to others and was impervious to getting sick again.

That’s far from certain, and Twitter later flagged his tweet with a fact-check warning.

While there’s evidence that reinfection in unlikely for at least three months even for those with a mild case of COVID-19, very few diseases leave people completely immune for life. Antibodies are only one piece of the body’s defenses, and they naturally wane over time.

“Certainly it’s presumptuous to say it’s a lifetime,” said Dr. Albert Ko, an infectious disease specialist and department chairman at the Yale School of Public Health.

As to whether Trump could still be contagious, Ko said the White House appeared to be following CDC guidelines for when it is appropriate to end isolation after mild to moderate cases of COVID-19.

But Ko cautioned that those who have had severe cases of the diseases should isolate for 20 days. He noted that Trump was treated with the steroid dexamethasone, which is normally reserved for patients with severe COVID.

Dr. Marc Lipsitch, an infectious disease expert at the Harvard School of Public Health, said the doctor’s letter does not provide enough information to be assured that Trump is no longer infectious to others. He noted that Trump’s use of steroids could prolong viral shedding so the CDC’s 10-day standard may or may not apply.

“It is a judgment call,” he said.

The White House memo followed Trump’s first public appearance since returning to the White House after being treated for the coronavirus at a military hospital. Hundreds of people gathered Saturday afternoon on the South Lawn for a Trump address on his support for law enforcement from a White House balcony.

Trump took off a mask moments after he emerged on the balcony to address the crowd on the lawn below, his first step back onto the public stage with just more than three weeks to go until Election Day. He flouted, once more, the safety recommendations of his own government days after acknowledging that he was on the brink of “bad things” from the virus and claiming that his bout with the illness brought him a better understanding of it.

His return was a brief one. With bandages visible on his hands, likely from an intravenous injection, Trump spoke for 18 minutes, far less than his normal hour-plus rallies. He appeared healthy, if perhaps a little hoarse, as he delivered what was, for all intents and purposes, a short version of his campaign speech despite the executive mansion setting.

“I’m feeling great,” Trump told the crowd, before declaring that the pandemic, which has killed more than 210,000 Americans, was “disappearing” despite signs of surging cases in several states.

In either an act of defiance or simply tempting fate, officials organized the event just steps from the Rose Garden, where exactly two weeks ago the president held another large gathering to formally announce his nomination of Judge Amy Coney Barrett to the Supreme Court. That gathering is now being eyed as a possible COVID-19 superspreader as more than two dozen people in attendance have contracted the virus.