White House chief of staff Mark Meadows told ABC News the determination whether to release President Trump from Walter Reed Medical Center will be made later on Monday between the president and his medical team.

While a determination has not been made as of yet, Meadows says he's "optimistic" Trump will be back at the White House later in the day on Monday.

Doctors on Sunday also said at a press briefing that they were hopeful that Trump could be released on Monday.

-ABC News' Katherine Faulders

President Trump, who is still at Walter Reed Medical Center receiving treatment for the coronavirus, fired off a series of voting and election-related tweets on Monday morning.

Trump tweeted about tax cuts and what he says would happen if Democrats were in charge.

He also appealed to voters in Virginia, where Trump claims the governor is trying to "obliterate your Second Amendment."

Dr. James Phillips, chief of disaster medicine at George Washington University Hospital and a non-military attending physician at Walter Reed Medical Center, spoke to Amy Robach on "Good Morning America" on Monday about the potential consequences involved in the president's SUV ride near Walter Reed in Bethesda, Maryland.

Philips, who is not treating the president, tweeted on Sunday that he thought the event was "insanity" and that it risked the health and lives of the Secret Service agents involved in the spectacle. He expanded on his thought process early Monday morning.

"I have serious concerns that in any automobile, masks or not masks, there's a very high risk of transmission," said Philips. "And then add into the mix that that's not any vehicle. That's a hermetically-sealed vehicle that is designed to be impenetrable to chemical attacks. Therefore the amount of circulation inside is even poorer than we would expect from a normal vehicle. And as a physician, we look at the decisions we make as risks versus benefits."

Philips continued: "I don't know what the benefits of this political stunt were, but I do know what the risks were. And my concern is that perhaps the secret service agents that were inside don't know the full risk of what they were up against there and what the real threats were. And so far as the military and Johns Hopkins physicians who are taking care of this patient, they're excellent. But they're also under undue pressure and a lot of influence outside of that normal physician-patient relationship."

When Philips was asked about whether or not the American public should be concerned about the information they are receiving about the president's health, Philips said that the doctors and nurses involved in Trump's care have the utmost of integrity.

"The president is a patient," explained Philips. "He has a right to privilege. But it's difficult whenever the information provided to the constituents is filtered through a lens of trying to paint a rosy picture. And I don't think that people were being dishonest. I just think that there's difficulty whenever you're pressured to say certain things and thrust into a job that these doctors were never expected to be thrust into."

Sources tell ABC News that President Trump was in good spirits Sunday, and was insisting that he wants to leave Walter Reed Medical Center as soon as possible.

Aides are pushing Trump to relax, sources say.

A timetable on Trump's release was still not finalized as of Sunday night, sources said. Doctors said earlier Sunday that Trump could leave the hospital as early as Monday.

ABC News' Katherine Faulders and John Santucci