There was something discussed quite a while ago that the Jan. 6 committee did not meet the legal requirements to force subpoenas. It was something to do with the party makeup of the committee. Does anyone remember?
The House has rules for forming committees. The rules have ZERO fore of law, and are purely internal agreements that supposedly give the minority party a voice in the process. But the minority on Congress is like the dissent in a court case. “Losing side.” This committees was formed in contravention to a rule that says the minority party gets to pick committee members. The GOP picked zero of the people on this committee.
If a majority of Congress issues a subpoena, it is presumed legit. I can;t imagine a court declaring the subpoena to be illegit on account of the makeup of the committee.
And the hook that there is a need for legislative purpose is so easy to meet that the hook might as well not exist. All that has to happen is for the committee to say “legislative purpose” and that that requirement is met, no matter what the committee is actually doing.
Court might say “if the people don;t like it, they know how to elect a different congress.” That exposes another fiction, that either party has integrity.