What’s to investigate? You have a bunch of anonymously sourced claims put forward by media hostile to President Trump. Unless some of these “sources” come forward, you can’t have an investigation. What you guys would like is for the Congress to haul administration officials before a committee and ask them about about unsubstantiated rumors.
That is exactly like the McCarthy hearings of the 1950s.
The alternative is to jail reporters who won’t name their sources. No Congress person wants to do that. So an investigation is a non-starter unless some of those “high officials” step up.