There were no answers, either, on when Mr. Trump last tested negative for the virus — a crucial piece of information that the White House and Dr. Conley have refused to answer and would establish the known state of Mr. Trump’s health before the presidential debate last Tuesday or before he attended a fund-raiser in New Jersey on Thursday. The White House first made public that Mr. Trump had tested positive early last Friday.

Two officials maintained that Mr. Trump had been tested before the presidential debate, but the White House has yet to affirm that.

White House officials conceded on Tuesday that there had been an impression created that Mr. Trump was getting tested every day, and a reliance on testing as if it were a curative measure as opposed to a diagnostic.

Yet the president himself was not tested every day, according to two people familiar with the practices. A senior administration official would only say on Tuesday that Mr. Trump was tested “regularly.” Mr. Trump himself told reporters in the White House briefing room in July that “I do take probably on average a test every two days, three days.”