Public health experts and epidemiologists say that it is helpful to know that Trump’s onset of symptoms came roughly a week ago. But establishing when he last tested negative would fill in a critical piece of the puzzle and help determine whether Trump was contagious last week during travel to the presidential debate in Cleveland, a rally in Minnesota or a fundraiser in New Jersey.

It would also provide a clearer timeline for when it might be safe for Trump to interact with others again.

“We have to know when the president first knew he was exposed to infection as a close contact, when he tested positive, when symptoms first appeared, when there was a negative test, and when that negative test was confirmed through state-of-the-art PCR testing,” said Lawrence Gostin, a professor of global health at Georgetown University.

“Because the White House is keeping the public in the dark about all these relevant facts, it is impossible to know if it was safe for the president to attend political events including the debates and Rose Garden nomination of Amy Coney Barrett, as well as when it is safe for him to leave isolation now,” he continued.