Updated at 7:59 p.m. ET

President Trump's hospitalization for COVID-19 casts unprecedented uncertainty on the presidential campaign's final stretch.

There are 30 days until Election Day and millions of votes have already been cast.

Trump is being treated at Walter Reed National Military Medical Center, forced off the campaign trail. Meanwhile, Democratic nominee Joe Biden, who debated Trump on Tuesday night, about 48 hours before the president disclosed his positive coronavirus test, is navigating how to campaign effectively while his opponent is in the hospital.

On Saturday, the Trump team launched Operation MAGA, aimed at maintaining the energy of its campaign without the president at the helm. The campaign has said it will host virtual events until the vice presidential debate in Salt Lake City on Wednesday.

Following that debate, Vice President Pence — who tested negative for the coronavirus again on Sunday — will do an in-person campaign tour through key swing states, starting in Peoria, Ariz., on Thursday.

"He'll be hitting the trail in Arizona, will probably be in Nevada, he'll be back here in D.C., and he's going to have a very full, aggressive schedule as well as the first family, Don, Eric, Ivanka," Trump adviser Jason Miller said on NBC Sunday. "And we have a number of our supporters, our coalitions: Black Voices for Trump, Latinos for Trump, Women for Trump. The whole Operation MAGA will be deploying everywhere."

Trump campaign manager Bill Stepien has also tested positive for the coronavirus.

The 77-year-old Biden returned to the campaign trail Friday, after saying that he had a negative coronavirus test — and though he shared a debate stage with Trump for more than 90 minutes.

In Michigan, Biden offered Trump well wishes — and a broad message about the virus.

"This is not a matter of politics," Biden told a small audience outside a union hall. "It's a bracing reminder to all of us that we have to take this virus seriously; it's not going away automatically. We have to do our part to be responsible."

In Michigan, Biden kept his mask on while speaking outdoors. His campaign says it will disclose the result of every coronavirus test Biden takes.

"We have adhered to strict and extensive safety practices recommended by public health experts and doctors in all of our campaigning — including social distancing, mask wearing, and additional safeguards," campaign spokesperson Andrew Bates said in a statement. "Vice President Biden is being tested regularly, and we will be releasing the results of each test."

On Sunday evening, the campaign announced that Biden tested negative that day.

Biden and his wife, Jill Biden, travel to Florida Monday for events, including an NBC News televised town hall on Monday night from Miami.

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