WASHINGTON — President Donald Trump tweeted early Friday that he and first lady Melania Trump have tested positive for COVID-19, almost certainly cancelling planned rallies in Tucson and Flagstaff next week and throwing the presidential campaign into a new uproar.

“We will begin our quarantine and recovery process immediately. We will get through this TOGETHER!” Trump tweeted.

White House chief of staff Mark Meadows told reporters Friday morning that the president is experiencing mild symptoms, but is in “good spirits” and “very energetic.”

“We have a president who not only is on the job, will remain on the job,” said Meadows, who spoke without a mask, saying he tested negative. “I’m optimistic that he’ll have a very quick and speedy recovery.”

Trump was scheduled to hold campaign rallies in Tucson on Oct. 5 and Flagstaff on Oct. 6. The events haven’t yet been officially called off, but the president said he was quarantining inside the White House for 14 days because of his diagnosis.

Late Thursday, Bloomberg News had reported that Hope Hicks, a close aide to Trump, had tested positive for the virus. Hicks had traveled to and from the presidential debate in Cleveland on Air Force One with Trump and also traveled to Minnesota with him, Bloomberg said.

Trump has repeatedly questioned the efficacy of wearing a face mask and other safety precautions, contradicting top health officials in his administration, and is rarely seen wearing one as he presides over large rallies packed with maskless attendees. 

At Tuesday’s debate, Trump said he wears one when he “needs to,” and derided Biden for routinely wearing a face covering. He has insisted that his approach is fine because those close to him are tested every day.

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Democratic presidential nominee Joe Biden, who shared the debate stage with Trump on Tuesday, posted on Twitter Friday that he and his wife, Jill, tested negative for the virus. “Thank you to everyone for your messages of concern,” he said. “I hope this serves as a reminder: wear a mask, keep social distance and wash your hands.”

In addition, Dr. Kevin O’Connor, the Bidens’ physician, issued a statement through the campaign. “Vice President Joe Biden and Dr. Jill Biden underwent PCR testing for COVID-19 today and COVID-19 was not detected,” he said.

Earlier Biden wished the president and first lady a swift recovery.

Vice President Mike Pence’s press secretary tweeted that Pence and his wife, Karen, tested negative for the virus on Friday morning.

Sen. Mike Lee, a Utah Republican, tweeted Friday that he, too, has tested positive for COVID-19. Lee had met on Tuesday with Supreme Court nominee Amy Coney Barrett and posted a photo on Twitter showing that meeting, in which neither of them were wearing masks.

House Speaker Nancy Pelosi, D-Calif., said Friday morning that she was praying for the president and his family, adding that she hoped the “tragic” situation would prompt “a transition to a saner approach” to minimizing the risk of infection.

“Maybe now that people who see the president of the United States with all the protection that he has, and the First Lady, still having this exposure, it might be … a learning experience,” Pelosi said during an interview on MSNBC. “But more than learning, it has to be something that’s acted upon.”

Pelosi said she was tested Friday out of “an abundance of caution,” but did not have the result yet. Her only contact with White House officials in recent days was negotiating over another coronavirus relief package with Treasury Secretary Steve Mnuchin, who announced he had a negative test Friday morning.

A memo from Dr. Sean P. Conley, the president’s physician, said he received information on Thursday night that the president, who at 74 would be at high risk for complications from the virus, and Melania had tested positive for COVID-19.

“The President and First Lady are both well at this time, and they plan to remain at home within the White House during their convalescence,” Conley wrote.

“The White House medical team and I will maintain a vigilant watch, and I appreciate the support provided by some of our country’s greatest medical professionals and institutions,” he said. “Rest assured I expect the President to continue carrying out his duties without disruption while recovering, and I will keep you updated on any future developments.”

Trump’s updated schedule for Friday includes hosting a 12:15 p.m. phone call on COVID-19 support for vulnerable seniors.

On social media Friday morning, Arizona members of Congress from both parties reacted to Trump’s diagnosis, wishing him a quick recovery.

“Wishing full and quick recoveries for the President and First Lady,” Sen. Kyrsten Sinema, a Democrat, tweeted.

Republican Sen. Martha McSally also said she was “praying for a swift recovery for the President and First Lady.”

GOP Reps. Paul Gosar and David Schweikert both said they were sending “thoughts an prayers” to Trump and his family.

Meanwhile, Rep. Andy Biggs urged Trump to take hydroxychloroquine to treat his illness. The medicine, which has for decades been used to treat malaria and other sicknesses, has been urged as a COVID-19 panacea by conservatives — including both Biggs and Trump — since the early days of the pandemic. However, there is no scientific evidence that it actually helps treat the illness, and Trump’s Food and Drug Administration in July cautioned against its use to treat COVID-19 because it caused serious heart issues.

“I encourage them to take hydroxychloroquine to assist with their recoveries, & I am confident that they will be resuming their normal routines in the very near future,” Biggs wrote.

The president’s positive test result comes days after he and Biden met for their first debate. The two men did not shake hands and stayed on opposite sides of the stage, which was in a large atrium on Case Western Reserve University’s campus.

Official safety precautions for that event, co-hosted by the Cleveland Clinic, largely focused on the audience, which was much smaller than usual for a presidential debate. The roughly 80 audience seats were spaced out from each other, and those seated had to test negative for coronavirus. Those in the audience could be seen wearing masks, with the exception of Trump’s family members and top aides.

A White House spokeswoman tweeted Friday morning that Trump’s daughter, Ivanka Trump, and her husband, Jared Kushner, who were both in the debate audience, tested negative Friday morning.

Jim Small contributed to this report.

***UPDATED: This story has been updated to include additional information and comments.