Codes of Civil Procedure sometimes have the requirement of this part of the process codified right in the law itself. You have to follow it, like a presuit request to say, retract libel.
What I don't get is the new, strange making up of procedure just to weasel out of jeopardy. They are literally making it up as they go. "Absolute immunity." And, because there is so much presidential power, they are doing it with apparent impunity. They are unafraid of the consequences, whereas you or I would be arrested for disobeying a subpoena.
The GOP clearly think they are above the law. They have this criminal ordering them not to talk. You almost get the impression that they have all done something criminal. Why can't they just show up with their own lawyer, even if he has to stay outside, so they are covered with the advice of their attorney? Ahhh, they are afraid of Trump and his vicious demeanor. Cowards.
You know, I'm on Pelosi's side, but she is very cautious and highly unlikely to actually have any of them arrested. If the procedural facts are correct, she should just do it. Trump can't pardon them for contempt of Congress. They are all doing it now, however, and they are effectively above the law. Party Over Country, and loyal to the Dictator. Just awful.