From the conclusion of Does Executive Privilege Apply to the Communications of a President-elect? (LSB10094, March 8, 2018):
Even if, for purposes of argument, the privilege is viewed as extending to certain communications between a President-elect and his transition staff, it nevertheless would seem arguable that the privilege may apply with less weight given that such an extension would appear to lack the same direct grounding in the Constitution that characterizes the privilege for incumbent Presidents. Courts have previously identified a variety of situations in which covered communications receive diminished protections; for example, after significant time has passed, when the incumbent president does not support the assertion of a former president, or where the President has made public disclosures about the communications. If this reasoning were adopted, it would likely influence the weight a reviewing court would accord to the President-elect’s “confidentiality interests” when balancing those interests against Congress’s need for the communications as part of a congressional investigation.