I'm still trying to understand this whole subpoena thing for an impeachment 'probe' where no vote is taken by the House of Reps to move forward on it. House rules apparently stipulate that a committee chairperson can issue subpoenas if they have jurisdiction over the matter in question, but the secrecy involved in this case and the seeming denial of Due Process for the President and the Executive Branch makes the whole thing look like a witch-hunt in search of a crime to prosecute. [Didn't Pelosi identify no fewer than 6 committees that will have some jurisdiction in the impeachment probe?] Far as I can tell, House rules do not require a full vote, which has always been done in every other instance related to an impeachment. I'm not sure the courts can dictate to the Congress how to do their business, but they also may not require the President to comply with a subpoena from just one person either, absent the authorizing House vote. Congress has the power of subpoenas with which to perform their necessary legislative functions, which includes impeachment, but there's gotta be some restrictions to prevent abuse of a subpoena, just like there are restrictions on executive privilege that the President can use to deny the release of transcripts, documents, memos, and the like, or the testimony of certain individuals. I do not think the Courts will be in favor of what the Dems are doing in this instance.
Funny, I haven't seen an impartial written description of what currently is allowed and what could be denied, so I guess the whole thing will wind up in the courts. Probably all the way to the SCOTUS. Sooner or later, the worm will turn and a democrat will be elected to the WH with a GOP House, and what was good for the goose will certainly be equally good for the gander.