In the seminal case of United States v. Nixon (1974), the Supreme Court held that President Nixon himself was required to produce information that was (i) in his possession, (ii) relevant to a criminal investigation, (iii) related to activities he undertook as president, and (iv) covered by executive privilege. Here, while the information at issue is similarly relevant to a criminal investigation, it is by contrast in the possession of a third party (the accountant), not related to Trump’s activities as president, and not covered by executive privilege.
The court did not reject the possibility that there may be some presidential immunity (during the term of the presidency) from the burdens of criminal investigations and prosecutions. Nor did it attempt to outline what the parameters of such immunity may be. The judges merely held that, even assuming some degree of immunity, it does not apply to a third party’s production of unprivileged information that is not germane to the president’s conduct in office, and that is related to an investigation the district attorney is within his jurisdiction to pursue.
The president’s private lawyers indicate that an appeal to the Supreme Court is the likely next step. I have some doubt that the justices will agree to hear the case, in light of the narrowness of the Second Circuit’s ruling, along with the facts that (a) the subpoena is not directed to the president personally, and (b) it is not necessary to grapple with the nature and potential scope of presidential immunity in order to decide that any such immunity would not extend to the accountants.