Found this article about how EP works in USA. It's from 2008, a paper about EP written for the australia senate, who were concerned that the underlying legal issues apply everywhere.
tl;dr summary:
the law is not settled. Courts have tended to leave EP as a political matter between legislature and executive. However the judiciary is the sole arbiter of whether EP is justified. Trump asserting EP means congress cant prosecute trumps staff for contempt of congress since they are properly following orders.
Congresses' remedy is to sue people in a minor court first, to adjudicate whether they can obey trumps orders or not.
Found this article about how EP works in USA. It's from 2008, a paper about EP written for the australia senate, who were concerned that the underlying legal issues apply everywhere.
["Legislative Power and Executive Privilege in the Courts"]https://www.aph.gov.au/About_Parliament/Senate/Powers_practice_n_procedures/pops/pop49/courtlegislativepowerandexecutiveprivilege)
tl;dr summary: the law is not settled. Courts have tended to leave EP as a political matter between legislature and executive. However the judiciary is the sole arbiter of whether EP is justified. Trump asserting EP means congress cant prosecute trumps staff for contempt of congress since they are properly following orders.
Congresses' remedy is to sue people in a minor court first, to adjudicate whether they can obey trumps orders or not.