New York Times report (update: Another report from AP)

It's notable that he has symptoms at all as many people who get the virus are asymptomatic. Given that he has them, it likely means he was exposed around Tues-Wed. It also means that he will be out of action for at least a week.

The report cites two people familiar:

The president has had what one person described as cold-like symptoms. At a fund-raiser he attended at his golf club at Bedminster, N.J., on Thursday, where one attendee said the president came in contact with about 100 people, he seemed lethargic.

A person briefed on the matter said that Mr. Trump fell asleep at one point on Air Force One on the way back from a rally in Minnesota on Wednesday night.

The report says his treatment plan is still being discussed and they are considering a national address or videotaped statement to demonstrate he was functioning.

Update: A second report from AP says he has mild symptoms.