It is not surprising that Congressman Luetkemeyer and some of his Republican colleagues invaded the House Intelligence Hearing on impeachment. This was a stunt to show their loyalty to the president in spite of the mounting evidence that the president has committed an impeachable offense. The Republicans set up the rules for secret hearings in the 2015 Benghazi Hearings and now refuse to be bound by rules signed off by John Boehner. In both the Clinton and Nixon impeachment investigations, witnesses were questioned privately before public testimony. Republicans on the House Intelligence Committee (some who also invaded the hearing) and their lawyers were free to question the witnesses thus ensuring due process in the private hearings.
Republican members of the Intelligence Committee and their lawyers are now participating in the public hearings of witnesses. If articles of impeachment are passed the president will have his own team of lawyers in the Senate trial. Luetkemeyer complains about lack of access to non-classified documents that are now being released to the public. Democrats have subpoenaed documents and want testimony from Rudy Giuliani, Mike Pompeo, John Bolton and Mick Mulvaney. Mulvaney has already admitted there was a quid pro quo before walking back the statement and simply asked the Democrats to "get over it." According to this reasoning, it is perfectly OK to ask for American citizens to be investigated by a foreign government as a political favor. Even without a quid pro quo, this gives a foreign nation too much power over American citizens and our foreign policy.
The president hides appointees behind executive privilege to prevent testimony. My conclusion is that these officials want presidential protection out of fear of perjuring themselves and to protect the president. This is the same type of non-cooperation exhibited by Richard Nixon until the courts forced him to cooperate with the impeachment investigation. Trump appointees want to stay away from any further testimony that directly links the president to attempted bribery of Zelensky that would harm his 2020 re-election campaign.
Instead of cooperating Trump has attacked witnesses as they are testifying which some have construed as witness tampering. He has also attacked the whistleblower stating that "you know what we used to do to spies," which has prompted his lawyer to order a cease and desist. The whistleblower is entitled to anonymity under the law.