SANFORD, Fla. (NewsNation Now) — President Donald Trump returned to the campaign trail for the first time since receiving coronavirus treatment. Democratic presidential nominee Joe Biden also traveled to Ohio on Monday.

Trump, who had been sidelined after he was diagnosed with COVID-19, hosted a rally at Orlando Sanford International Airport in Florida.

The former vice president delivered an afternoon campaign speech in Toledo and visited Cincinnati for a voter mobilization event.

Biden extended his advertising presence in Ohio last week, adding money notably to radio in rural western counties and in the state’s eastern and southeastern Appalachian counties, where Trump won big four years ago. The president won the state over Democrat Hillary Clinton by 8 percentage points in 2016.

Vice President Mike Pence also campaigned in Ohio on Monday. He made a “Make America Great Again” campaign stop in Columbus this afternoon.

Over the weekend, the president claimed on Twitter and in an interview on Fox News Sunday that he’s “immune” from the virus after White House doctors said he’s no longer at risk of transmitting COVID-19.

Twitter flagged the Tweet with a fact-check warning, saying it violated the company’s rules “about spreading misleading and potentially harmful information related to COVID-19.”

Some medical experts have been skeptical that Trump could be declared free of the risk of transmitting the virus so early in the course of his illness. Nor can he be completely assured of immunity following his illness.

In a memo released Monday, President Trump’s most recent COVID-19 tests came back negative, on consecutive days, according to White House Physician Dr. Sean Conley.

Dr. Albert Ko, an infectious disease specialist and department chairman at the Yale School of Public Health, 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, not just 10 days as Trump has done. He noted that Trump was treated with the steroid dexamethasone, which is normally reserved for patients with severe COVID-19.

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 confident that Trump can no longer infect others. He said Trump’s use of steroids could prolong viral shedding so the CDC’s 10-day standard may not be enough.

The president’s physician said that Trump showed no evidence of his illness progressing or adverse reactions to the therapy he received.

Both the Trump and Biden campaigns’ events Monday come as the confirmation hearings for the president’s Supreme Court nominee, Judge Amy Coney Barrett, begin in the Senate.

The hearings began Monday and are scheduled through Thursday.