Well the Trump Administration is saying this morning that unless there is a full House vote to initiate impeachment hearings they will not regard any subpoena, inquiry or requests for information to be valid and they will not comply with them. No member of the administration will appear before any committee.
The reason, primarily, is that after the House votes to initiate hearings the Republicans are then allowed to call witnesses, question witnesses, introduce material into the record etc. Its only fair and it has been the precedent in 4 previous impeachment proceedings.
Fish or cut bait Nancy.