The court’s ruling that Manhattan District Attorney Cyrus R. Vance Jr. had the right to obtain them was surely correct. Vance is investigating whether the Trump Organization broke New York law by falsifying business records to hide payments to women Trump allegedly had affairs with in exchange for their silence. In pursuit of that, it is essential that Vance obtain the records whose falsification he is trying to establish. By holding that he can, the court simply followed precedent and general principles of criminal law.
It is irrelevant whether that investigation is politically motivated. (Vance is a Democrat.) Politically motivated but valid investigations are not a novel feature in the U.S. legal system, where state and local district attorneys are elected and federal prosecutors frequently have sought elected office. President Bill Clinton faced a similar civil suit financed in part by his political opponents from a woman, Paula Jones, who alleged he sexually harassed her while a state employee. Courts in the Clinton case held that he had to testify under oath even though he was president because no person is above the law. Requiring Trump to produce the highly relevant information in Vance’s investigation is simply the logical consequence of the decision in Clinton’s case.
The same considerations clearly do not apply in the pair of cases involving the congressional subpoenas. Those committees, as the majority opinions noted, did not provide a specific reason Trump’s returns were directly relevant to their inquiries.