The White House said the visit of "a few days" to Walter Reed National Military Medical Center was precautionary and that Trump would continue to work from the hospital's presidential suite, which is equipped to allow him to keep up his official duties.
Hope Hicks, a former White House communications director who returned to the administration as a counsellor to Mr Trump earlier this year, travelled to and from this week's presidential debate in Cleveland, Ohio with him. "God bless you President Trump & our wonderful First Lady Melania".
The White House did not immediately confirm the diagnosis, however Trump later acknowledged it in an interview with Fox News' Sean Hannity, saying Hicks "did test positive".
Also in a tweet shortly, the First Lady said: "As too many Americans have done this year, @potus & I are quarantining at home after testing positive for Covid-19. In the meantime, we will begin our quarantine process!"
Ms Hicks had accompanied Mr Trump to OH for the presidential debate on Tuesday and to Minnesota for a campaign event on Wednesday. Earlier this summer, Herman Cain, a previous candidate for the Republican presidential nomination, died after attending an indoor Trump rally in Tulsa, Oklahoma, this summer. "And when they come over to you, it's hard to say, 'stay back, stay back.' You know, it's a tough kind of a situation, it's a awful thing", he said.
Trump's schedule has been scrubbed of events tomorrow aside from a phone call on COVID-19 support with vulnerable seniors.
Trump's Refusal to Condemn Proud Boys at Debate Reflects His Electoral Strategy
On Wednesday, when asked to clarify his remarks, President Trump told reporters he doesn't know who the Proud Boys are. Proud Boys is a far-right organization that admits only men as members and promotes and engages in political violence.
Soon after it was confirmed, many took to Twitter and reacted - in their own manner - to the news.
Trump then said he has had "no negative effect" from massive campaign rallies with thousands of attendees not adhering to social distancing recommendations amid the ongoing pandemic.
The first town hall question.
While its ultimate effect on the race remains unpredictable, the thunderbolt news had immediate electoral consequences for Trump, forcing him to cancel a rally planned later Friday in key swing state Florida.
Biden is scheduled to campaign in MI on Friday.
Biden has criticized Trump sharply for his response to the pandemic; the president has praised himself and his team. Others who will be in close proximity to the president and vice president, including reporters, are also tested every day.
Trump tweeted out the surprise announcement in the early hours of Friday.
White House deputy chief of staff Dan Scavino, counselor to the president Hope Hicks and senior policy adviser Stephen Miller walk across the South Lawn before departing the White House late last month. Others hastened to add that Hicks is often seen in public without a mask.