I was prepared to believe that Trump did have Covid and still think he has it, but the timelines indicated by the "official" view from the President's camp look very suspicious. This article;-

https://www.bbc.co.uk/news/election-us-2020-54413879

asks relevant questions, with the reluctance of the Trump camp to say when he last tested negative making me believe that it's entirely possible that there was a positive test before Thursday night/Friday morning and the feeling first of all was that things could stay as normal for the President unless his symptoms got worse - especially given the personality of the individual involved.

A big difference between Trump and "ordinary mortals" is that he will have been tested for the virus on a very regular basis and so it seems virtually impossible that the test which led to the announcement that he had Covid just four days ago would have been his first one that week.

People who know better than me will be able to answer the question do patients normally have to be given oxygen within two or three days of learning that they had the virus, but my feeling is that they don't unless they have had the virus for a while before having it confirmed..