“The combination of the two factors makes Biden a close contact, even if the letter of the law doesn’t consider him one,” Dr. Marr said.
Mr. Biden tested negative for the virus twice on Friday, the Biden campaign said. He was not tested on Saturday and left his home for part of the day, going to a theater to participate in a virtual event and a church to attend Mass. The campaign announced his latest negative test result on Sunday night. Pressed on CNN about the frequency of Mr. Biden’s coronavirus tests, Ms. Sanders said the candidate was “tested before we travel.”
In the coming days, the Biden campaign is aiming to balance health precautions with continued travel in Florida on Monday and in Arizona on Thursday. Yet Mr. Trump’s positive test has plainly injected an extraordinary measure of uncertainty into the race.