Here’s a bit more detail on how the word leaked out. From the link below:
In a recording of a radio message from D.C. Fire hazmat personnel who responded to the scene Sunday night, a first responder can be heard saying the substance tested positive for “cocaine hydrochloride.” The message was posted by the website OpenMHz, which records and archives radio dispatches by police, fire and EMS agencies.
https://www.cbsnews.com/news/white-house-cocaine-west-wing-secret-service-investigation/
I recall reading someplace that the first responders initially reported by radio that the cocaine was found in the library located within president’s private residence. This was widely reported by the MSM. A few hours later the WH changed the location to the heavily traveled West Wing storage area, and when questioned about the discrepancy with the initial report, the WH claimed that the first responders had no authority to speak on the matter. Now we have been told that the dope was found in a lower level of the West Wing.