I saw it reported that one of the Congressman on the committee says that other whistleblowers have been in touch with them. For those who doubt that that those who have already testified are mistaken in their beliefs, we may begin to get more of the details filled in if more come forward.
The thing about a cover-up like this is that if even one person of conscience breaks the Code of Silence, then others are likely to be emboldened to do the same.
While so far there seems to be no legal basis for impeachment, if additional details continue to show the untrustworthiness of those in charge, it will be a blot on the first black President's term. One could forgive incompetence more easily than prevarication for self-interest.