Two Republican senators and three White House journalists have tested positive. There is a significant overlap between who got these recent positive tests and participants of Barrett's nomination announcement last Saturday. Barrett herself tested negative and there are reports that she had COVID-19 and recovered a few weeks ago.
If Barrett had it and has since recovered, someone in her household may have brought it to the White House.
When the leader of the free world has a potentially deadly virus, it is best for him to be in a situation in which he is closely monitored, and that doctors can act quickly in case his situation deteriorates. Trump is continuing to work while in the Hospital, and put out a video saying that he is feeling better.